From a different thread, here is a comment about how I calibrate my system:
--------------------------------------------------------
Audyssey alone probably works great with the standard 5.1 THX set up where all main speakers are small and send all bass to one subwoofer. I say this because the Audyssey listens once and makes it's adjustments, it doesn't listen afterward to make sure everything sounds correct. If you have more than one subwoofer, Audessey doesn't take in to account that at some frequencies the subs might be out of phase and you get no sound, no matter how high the volume level is.
With my system I have the 2 12" subwoofers in the main speakers and also 2 outboard subs. When the Audyssey gets done with it's testing and then I play my test cd's, there are always frequencies where the subs don't play well with each other. As an example, my speakers might be level at 85db from 20khz down to 60hz, then 50hz has nothing (even though the drivers are shakin' their butts off). Then 40hz might be back up to 85db, then 32hz has nothing.
I use my outboard sub eq's to adjust the phase, crossover, and volume for each sub and I can get them both to work together again.
So how I make adjustments is:
1. (with Audyssey off) level all my speakers from 20khz down to 20hz with outboard eq's.
2. run Audyssey set up.
3. listen with test cd's and re-level all speakers with outboard eq's (usually Audyssey's levels will be good from 80hz on up, but I always have to play with several sub frequencies).
----------------------------------------------------------------------
Although my ATI amp kicks butt, the outboard equalizers have the biggest impact on the sound. Actually I never intended to get an amp but when trying to connect my eq's back in '03(?), I found that an outboard amp was needed because the cabling had to go from the AVR--> into the eq--> then into an outboard amp (originally I was thinking the cabling could go from the eq back into the AVR again, but I was mistaken). So, I had to buy an outboard amp.
The eq's get everything pretty flat (much, much flatter than Audyssey can) but then I still run the Audyssey because it's supposed to correct timing issues and other stuff. The eq's make a huge difference that is noticeably better than the non eq'ed sound. The Audyssey makes a very small difference that I really can't tell if the sound is better or not, but because Audyssey is supposed to help, I leave it on.
If I didn't use outboard eq's, then the Audyssey would probably help to flatten the speaker output and would help to make the system sound better.
As far as the sound of the ATI amp:
I didn't do any critical before and after listening tests. I did listen to one track before and after: the 1812 Overture conclusion that uses live canon fire. After the amp was added, and the AVR volume set to the same volume setting, the canon fire sounded much more clean and I think had a little more oomph. The big difference was that the amp let me turn the AVR volume much higher while retaining a clean sound. There was probably a lot more 'air' and stuff to the upper range, but I really wasn't listening for it.
As mentioned earlier, the biggest and best improvement came from the eq's.