Piecing together a decent HT setup as I can afford it, need help with a plan!

First and foremost, you should add a Blu-ray player, preferably one that has, at the very least, a Netflix app. From there, perhaps look to upgrade your receiver to one that can either accept multi-channel (7.1 or 5.1) PCM over HDMI or can decode the newer hi-res, lossless audio codecs, such as Dolby TrueHD and DTS-HD Master Audio, and upgrade your speaker system to 5.1 or 7.1, depending on your room size and dimensions.

Amazon is currently selling a nice Denon HTIB (DHT-391XP) for under $320 that may be worth looking into.

As for Blu-ray players, my brand preferences are Panasonic, Sony, and Samsung. If price were no object, I'd spring for the Oppo.

The receiver and speakers you have now are far better than anything you will get in a $300 HTiB, so even though the receiver doesn't do the HD audio formats, I would keep it for now.  HTiBs are just a waste of money when you plan to upgrade beyond them.  You can get some larger Polk RTi speakers, like you were saying.  The Panasonic 65 does NOT have a regular digital audio output, only hdmi, so it basically will not work with the receiver you have now.

So, what I would do is add a BR player and the needed RTi speakers, then get a better sub.  Polk makes good speakers at a nice value, but their subs are not very good.  I would probably not upgrade the receiver until after those others are done, and get a decent one, not just the cheapest thing available.

I think using the Polks as back speakers is good idea. 5.1 will do for home theater in most cases. Possibly upgrading the front three speakers for starters could be your next step. If need be start with only the front two and save the center for later.  You need to go out an audition some speaker brands, here is a link to get familiar with different brand. Don't stop after the first page continue on to multiply pages. If you see something you like go to there web site and see if there is a dealer near you.

http://www.hometheater.com/category/compact-speaker-reviews

A Blu-ray players is also a good idea and the Panasonic BD 65 does have an optical digital out put that will work with your current receiver. It does not have a coaxial digital out put but the optical should work for you. You mentioned the Xbox what about PS3 as a Blu-ray player. 

I suggest considering a new receiver. It's not necessary; you've got a nice one. But you're in a place to switch to 100% HDMI connections. It simplifies your cabling, reduces the rats-nest behind the receiver, and may allow more choice on the Blu-ray player selection.

I was in a similar situation two years ago, and because my non-HDMI receiver was out of connectors, I could either buy a $200 Blu-ray player with the right TOSlink output, or get a new HDMI receiver and buy a $100 Blu-ray player. I found the receiver I wanted on sale, and did the upgrade. I changed everything to HDMI and sold the DVD player for $20.

I may need to be corrected on the Panasonic 65.  My folks had gotten a Panasonic player recently, and when I went over to hook it up, found it didn't have any digital audio outputs, even though Best Buy's site said it did.  Since they don't have a receiver with hdmi, they had to return it.  I thought it was a 65, but maybe it was a different one.  It is a brand new model and their regular price is about $100.

As Dave said, if you are running out of digital inputs, maybe you should look into a new receiver now.  If not, I still recommend waiting until toward most other stuff has been upgraded.  With the other items you currently have, upgrading the receiver now simply makes no sense, unless place cable simplicity over sound quality.  FWIW, I'm usually at odds with a lot of people here in this area.  I usually don't agree with the general attitude of updating codecs and processing first when the other equipment is in need of improvement.  I also generally think people spend too much on video equipment and too little on audio.

I'll say again.  Looking at the rest of the system, I just don't see a reason to update your electronics until you have a more complete speaker setup.

Building your own speakers can save you some money.  How much you can save really depends on the size and type of speaker. 

If you have some skills, some tools and the interest in doing the project, it is definitely worth consideration.  Speaker building is fun and very rewarding.  If it sounds like your cup of tea, I say -- go for it.  The standard speaker building cabinet material is 3/4" MDF.  Is that available at a reasonable cost in NZ? 

You will need some wood glue for the panels and polyfil for stuffing the cabinets (so they don't sound hollow) and of course, whatever drivers and crossover parts are required by the design.  I use half-lap joints in my constrution so I don't even need screws.  The cabinets are so strong that you can jump up and down on them.  You can use a proven design, as on the Parts Express website (or found all over the net) or you can start studying theory and design your own from the ground up.

http://www.parts-express.com/projectshowcase/projectindex.cfm 

You would need some cutting tools, preferably a table saw and some way to cut accurate driver holes.  You need some basic soldering tools and skills and some way to finish the boxes when they are done.  That's about it.

I run the DIII's from the PE link above.  As long as you get a 4 ohm stable receiver, they are a great value.  There are also hundreds and hundreds of other proven designs on the web and many different price points.

To save on shipping, you can use a car audio sub and a pro amp.  Can you find a dealer for Infinity or Resonant Engineering?  Depending on the model, you can use a Behringer or Nady amp for an awesome sub.

The Kappa Perfect is a proven sub that works in both car and home environments.

Marketing.  You have to look at the Theile/Small parameters to determine if a sub (car or home) will work for your needs.  There are a lot of guys that run Fi Car Audio and Resonant Engineering subs in their home.  Both are really marketed to the car audio guys.  The old Shiva and Tempest from Adire Audio started as home subs but the car audio guys found out how good they were.  The Dayton RS subs (from Parts Express) aren't marketed to either group.  They state their parameters and features and let the user determine if they fit.  Turns out that people are running them in their home and car.

Now that we know the driver doesn't matter, the enclosure does.  Car boxes are small.  Home boxes are large.  Hoffman's Iron Law (Google it) is at work.  You want extension (playing the low notes) so you either go big or through huge amounts of EQ and power at a small sub.  That costs money for parts and experimentation.

Sam,

It sounds like you found a new hobby!  Speaker building is a fantastic excuse to buy yourself a new router too!  If you know what a router is, you won't have any problem getting good results with this hobby.

I get my polyfil, which is usually "Dacron" at the local Wal-Mart in their sewing department.  It looks like a big ball of cotton in a plastic bag.  You could probably get it at any sewing supply store.  It is used to stuff pillows.

Here are a couple of links that you might find very useful at some point.

http://www.diyspeakers.net/ 

http://www.diyaudio.com/forums/loudspeakers/ 

Have fun.

Do you have any dealers for Resonant Engineering or Ascendant Audio?  You may have to look on some can audio forums dedicated to NZ to determine this.  You won't find these companies in large, retail stores.  What about the larger car audio companies like JBL or Alpine?  They have some subs that work well in the home.  Finally, if you are going to order from PE, why not one of their Dayton Audio or TC Sounds drivers?

http://www.haoleb.com/kappaperfect.htm

Ohhh, yeah, TC Sounds... something like this, Epic 12" (if it fits your specs)... http://www.parts-express.com/pe/showdetl.cfm?Partnumber=293-650

Put a couple of those back-to-back in an opposed, side-firing box.  Mmm-hmmm, that's the ticket!

That will keep your system kinda high-end, like your Oppo 93... nice choice there.

TC Sounds.  I know a little about their subs.  I have or had the following:

3 - 12" Epics - Sold under the Stryke Audio brand a few years ago.

1 - 12" TC9 - http://www.soundsplinter.com/rlp12_subwoofer_information.html (built by TC Sounds)

1 - 12" custom TC9 - http://s3.photobucket.com/albums/y78/rlj5242/Custom%20Sub%201/?albumview=slideshow (built it myself from TC Sounds parts)

2 - TC12 OEM - http://audiojunkies.com/forum/blog/3600-tc-12-oem-$195-shipped.html

3 - 15" TC-3000 - http://www.youtube.com/watch?v=W4zIxz8MdK8 I have 2 of the quad 2 ohm coil subs like the one in the video.  The odd one is a dual 2 ohm with a black cone that looks like the Axis subs from PE.

2 - db12's - http://www.youtube.com/watch?v=swfTp0L7iUU These were part of the old SVS cylinder subs.  I picked them up when someone upgraded to a better SVS driver.  I cloned the cylinder subs and traded the guy in the video for the black TC-3000 above.

1 - 12" TC7 - http://www.youtube.com/watch?v=33GESMbOMH8 - The motor (magnet) can be seen in my slideshow as the original frame/magnet I bought.  I only wanted the frame for that build.  I had a 15" TC-2000 top assembly where the original owner had buckled the aluminum cone.  I ripped the cone off and gently removed the coil/spider assembly.  Add a custom 12" basket and a surplus 12" cone and I built another sub.  Awesome little thing.  I traded it to the guy in the video for a classic Rockford Fosgate car amp.

1 - Elemental Designs E12A.22 - TC9 with a flat, honeycomb cone.  Never got to hear this one.  Damaged during shipping.

1 - Elemental Designs E10K.44 - TC2+ (same motor as an Epic) with a flat, honeycomb cone.  My cousin-in-law ran this in his truck.

4 - custom TC9 18's - TC9 motor from an E12A.22 coupled with 18" recone kits from Fi Car Audio.

1 - SVS 12" Ultra driver - The only TC Sounds underhund design.  An Audiomobile MASS motor (still had they label under the magnet boot) on a basket like my custom sub and an aluminum cone like the Epic.  Sold it to a guy in Ohio and it was lost in transit by FedEx.

4 - custom TC-3000 neo 15's - Build is in progress.  I have 4 very rare 3HP neodymium motors and 15" Axis style baskets.  Surplus cones from Sundown Audio with other spare parts.  These will be some monsters with close to 40mm of excursion.

4 - custom 12" LMS subs - Build is in progress.  Two motors are from the E12A.22 subs (TC9) and two motors from ssackett subs (like a TC9 but instead of dual 1" magnet slugs, these have triple .75" magnet slugs.  All else is machined the same)  Read up on the LMS at PE.  These have variable winding voice coils that lower distortion by flattening the BL (measure of magnet force) across the excursion of the cone.

1 - TC2+ 12" - Build is in progress.  Spare parts to build something similar to an Epic.

The other thing you could do Sam is look around to see if you could find any floor standers that are blown. Once in a while you can get lucky finding nice speakers that people abandoned because they are blown. Then you don't have to deal with tuning the box to get it just right, however you seem pretty excited so best of luck and definitely post back and let us know how they turn out!

First, not all of those are connected right now.  I'm only running dual TC-3000's right now.

Step 1 - How much space are you willing to sacrifice?  If it is not much more than your current sub then we need to look at a very high powered system (see Hoffman above).  If you can go big, then you have a much more efficient system that will easily play lower. 

Step 2 - Budget?  You are willing to ship drivers half way around the world so you seem committed to a quality project.

Now let me throw another wrinkle into the mix.  If you want to save space while having the best bass money can buy, you can go with an infinite baffle sub - http://ibsubwoofer.blogspot.com/ .  That link is one of hundreds covering the topic.  Start from the first post and read how they work and his final results.  Basically, you use another room or the attic as your enclosure.  No bulky box in your room.  On the other hand, you need more than one driver.

Also, this guy is a lot closer to you than I am - http://www.subwoofer-builder.com/ .  He may have have good sources of drivers at least from that large land mass to your west.

I'm assuming those are external dimensions.  Net volume of air will be much less than 4.8 cubic feet.  Based on that, only high motor force, low Vas 15" subs will work (if you want a 15).  How about the Dan Marx TC-3000 design http://www.danmarx.org/audioinnovation/tc3000.html  except use a Dayton 15" http://www.parts-express.com/pe/showdetl.cfm?Partnumber=295-468 ?  In fact, I'd recommend a pair of them powered by a Behringer A-500 http://www.parts-express.com/pe/showdetl.cfm?Partnumber=248-749 .  If you are short of floor space, stack them.

Advantages:

You are under budget by about $50

2 subs are always better than 1

Sealed subs have a nice roll-off and will play very low

No messy EQ required like with a lot of the TC subs

The LMS 15" and an EP amp (2500 & 4000 are exactly the same amp) would be a great combination but I would suggest adding a Feedback Destroyer as well.  TC drivers have a higher inductance.  Yes, they do things like copper on the pole piece to lower it but with a 3" or larger coil, it will never be as low as the Daytons I suggested above.  Plus an LMS driver will never work in an enclosure as small as you want.  The TC-9 motor is strong but not strong enough.

The BIC gets great amateur reviews as one of the best, under $200 subs.  Since it is a 12, it will push more air than a 10 with less effort.  Less excursion = less distortion.  Check Amazon because it was going for even lower last week.

My brother has the BIC V1220 and it seems pretty good for the price.

I have a Dayton HSU10 from the first batch sold a couple of years ago and it's definently a quality sub but it's listed frequency response is only 32 hz and that seems about right. I also have a couple of the original  Dayton 10" "mighty-mites" (25 hz) and they can go a little deeper than the HSU. The HSU10 seems like more of a hard hitting sub rather than a deep one. It does seem very detailed and accurate but I really don't feel qualified to evaluate subwoofers.

$188 shipped from Amazon looks like a good deal for the F-12. Of the two, I'd also get the BIC. The V1220 isn't the best looking thing out there, though. Kind of an uggly dark grey box. Very pedestrian looking.

BTW, the Allison AL10 from PE appears to be identicle to the Dayton HSU10 except the driver is near the bottom in the Allison with the port near the top. The amp looks to be the same as does the cabinet and grill from what I can see in the photos. I bet most subs in this price range could benefit from a better cabinet.