Check out the manual. If they aren't labeled left and right, they may tell you to manually swap the polarity of the wire you have going into one of them. Typically with dipole speakers, you want the forward-firing drivers to be in phase with the front speakers.
If space and absolute volume is not a concern, you might also consider a pair of $700-$1000 subs for smoother response across more listening positions. That opens up a lot more choices.
The frequency response is likely to be different, the largest difference being low end extension. But, since you already have the spare amp, might as well get your sub working again. Also, you may need something to attenuate the sub-out signal if your Carver amp doesn't have a trim control on...
The only consideration I can think of is if you can't give a sub's ports enough clearance from the wall. e.g. if you have a sub with rear firing ports and you have to put it 2 inches from the wall, you may want to consider a front or downfiring sub.
Also just to note, the dual driver models are 16/20/25 Hz selectable, whereas the single driver models are 12/16/20 Hz selectable. I've read that if you go down to only 1 port open, it's underported. So I think 16Hz is the optimum only if you have a single driver SVS. Corrections or additions...
The existence of good (great) products without THX certification is not "proof" that certification is overrated or that it doesn't mean much. What is your reasoning behind why you feel THX certification doesn't mean much? Certainly M&K (and others) must feel it means something, otherwise, why...
Really? I guess M&K, Atlantic Tech, and the Klipsch Ultra2 sets are all overrated, huh? You might tell all the post production studios how overrated it is that their M&K monitors are THX certified, and how it doesn't mean much. Look, I would never say you should get a speaker just because...
There is a difference between THX Ultra (the original spec, when there was only one), THX Select (what the Crystal speakers are), and THX Ultra2 (the updated original spec). One of the main differences between Select and Ultra(2) is a reduced requirement for controlled vertical dispersion...
Umm, no. Higher impedance numbers mean more resistance. Resistance isn't what makes an amplifier work harder. It's low levels of resistance, like a speaker that dips to 1 or 2 Ohms, because that means more current will be flowing. Perhaps you're thinking of wire guages, where a smaller number...
If you're on a tight budget, but think you might be able to spend more down the road, you should consider starting with a decent pair of speakers and a sub.
There are plenty of people who get great results from a losslessly encoded CD collection streamed to a squeezebox or the like (google that). I wouldn't worry too much about the difference b/w lossless music over a squeezebox vs. CD transport w/ outboard DAC. Your efforts (and dollars) will be...