Re: Onkyo 705 vs. 605
The typical street price difference seems to be around $200 or less. Only you can really decide if the additional features are worth it to you.
There are a few key differences that have been glossed over.
1) The 705 has a more sophisticated version of Audyssey.
2) It has preamp outputs should you ever decide you want more power.
3) By achieving THX Select certification, it's amplifier section is most likely a little more robust than the 605s.
4) It has more processing power. The 605 cannot apply 7.1 expansion to 5.1 hi-def audio (MPCM/TrueHD/DD+/DTS-HD). The 705 can.
Another unit worth considering, IMO, would be the newly released Yamaha RX-V663. Only 2 HDMI inputs like the 605, but the processing power is the equal of the 705 and it has Burr-Brown DACs (considered an upgrade over the Crystal parts used in the 705, by most). I believe the 663 also does 1080 upconversion of analog to HDMI. I've seen posts that say you can get the 663 from J&R for $399 delivered when ordered by phone.
-Brent