I sold the NR818 to stitch1 for $630.
I'm not a big fan of Audyssey. stitch1 and I spent hours last night turning Audyssey on and off listening to it back and forth. he liked it. I didn't.
He said he felt it had more midbass with Audyssey on. I said it sounded like someone boosted the treble by 4dB. Most voices sound like snakes hissing with Audyssey on to me. Music mode sounds horrible - it boosts treble by an additional 3dB or so (IIRC) over movie mode. Movie mode is better but still boosted the treble beyond my tolerance. During our movie watching section flipping it on and off neither of us could tell much difference, so the difference was noticed primarily in music. (we tried all genre's of music).
We graphed it on and off a dozen times. My synopsis was correct. Audyssey primarily boosts treble in my room - by about 5dB in movie mode and more in music.
I'll post some graphs this evening if I have a chance --- this week for sure. We used the full eight capture points in a mid room, small three seat bubble, with a tripod.
It may be my untreated room, it may be my ears --- but I don't like what Audyssey does to any of five sets of speakers (Crystal Acoustic, JTR Triple 8, ED Cinema 12, JTR Noesis, and Wharfedale) I've tried in my room on three different Onkyo Receivers (SR805, NR1007, NR818). stitch1 liked it --- so your mileage will may vary based on whether you like snakes or not.