The Audyssey MultiEQ is just fine on the 805. It is the same Audyssey software that is used in my $1800 Onkyo Pro PR-SC885P processor.
Audyssey MultiEQ is a very sophisticated room correction system that uses a supplied-microphone to take sound readings of your system in your room and processes the data through a complex algorithm to determine speaker placement, speaker frequency response, room bass nodes, and room reflections and then modifies the frequency response and channel delay settings inside the AVR to optimize your system's sound. It works great to equalize the bass in your room and to make all of your speakers blend seamlessly. As Cruz 123 points out, it does not always get the individual speaker volumes levels exactly right, so it is nice to have a Radioshack analog SPL meter to double check this after you run Audyssey. What it does in correcting bass nodes and room reflections is very impressive and cannot be duplicated through normal equalization methods. Definitely recommended.
The latest Denon and Onkyo products have an enhancement to Audyssey MultiEQ called Dynamic EQ. It is designed to 'dynamically re-balance' the frequency response at different volume levels so, for instance, the bass volume level is boosted at lower volume levels. I have not heard it; however, I have read posts on several forums about it and the comments are mixed - many do not like its effect andc choose to leave it disabled (just the Dynamic EQ function, not the MultiEQ).
I would not give this much consideration. The 805 will make you very happy.
