My 5.1 setup includes upper mid-range Polk F/C/Surrounds, and a powered Outlaw sub. The display is a Pioneer KRP-500M hooked to a PS3, Wii, HD-DVD player (ha) and HD cable box.
My first impression was that while the 818 gets warm, it's no where near the scorcher that the 805 was. Hopefully this results in much better component life, but we'll see.
As for the sound quality...I had spent many hours tinkering with Audyssey on the 805, and after giving it more than a fair shot, I had to turn if off after a while and ended up using it for setting distance/trims only. I am liking it MUCH better with the 818. I can't say that I'm completely sold on using it full-time yet, but it's definitely much more impressive. Bass response is much better and fuller, and the surrounds are far more active without seeming at all overbearing. This has resulted in a much greater sense of being in a high-end movie theater than before.
My only concern is that while Audyssey tends to do a great job of focusing and balancing the sound, it simultaneously tends to narrow/flatten it. Mid-range is definitely less "full" with Audyssey turned on (I am using Dynamic EQ as well). Is this normal? How do I know what I am hearing is the result of my system being more accurate? Obviously TVs lose a lot of punch when you take them out of torch mode and calibrate them. Is that what I'm experiencing here? Or maybe I require more tweaking? Or is it possible my rather oddly-dimensioned room isn't very suitable to Audyssey? Again, though, I am liking it much, much better than its older cousin on the 805.
Overall, I don't feel like I am missing anything in terms of sound quality coming from an 805, especially when listening at levels below reference, where the 818 definitely seems punchier. At 0dB I want to say that they are comparable, with the edge going to the 818. However, without the ability to do a direct A/B it's hard to be sure how big of a difference it is. I have yet to try it with music, which I've heard from others is where the biggest improvement lies in coming from an 805. I'm looking forward to seeing how it stacks up.
My biggest question at this point is:
Are there any "hidden" or must-adjust settings with the 818 that I should know about, whether for sound or video? Particularly I'm concerned about video quality. My display is professionally calibrated, so video fidelity is very important to me. I don't want the 818 taking it upon itself to mess around with an already-pristine signal, like from a Blu-Ray. I'm fine with it doing the processing for say, DVDs or the Wii. Is there anything I need to do to make sure that I am accomplishing this?