I had an Integra (by Onkyo) 5.3 (6.1 channel) receiver and upgraded to a Pioneer Elite SC-07. The difference was dramatic in both audio and video performance.
The SC-07 has switching class D amplifiers opposed to the Integra's linear solid state. Both receivers driving my 91dB sensitive Triangle Comets the Integra had less bass, is congested at higher listening levels, and ran much hotter, compared to the Pioneer. I've been involved with class D for some time and the Pioneer did not exhibit any of the AC related issues commonly related to class D operation. It creates no unwanted interference and is dead quiet considering it has a two prong captive power chord. Most of the other receivers features would be an unfair comparison due to technological advancements.
The Pioneer has a proprietary graphic/parametric room correction program. Finding a good comparison between the Pioneer and the Audyssey programs wasn't available at the time. Audyssey is licensed to other brands and offers different levels of functionality. I would be surprised if the audible differences at the simple user level would be much different, if at all. After running room correction I'm convinced that room correction is not only a terrific convenience but key to well balanced audio in a home theater environment.
Along with the Elite 151FD display and the BDP-05FD player the images are limited only by the quality of the media its being fed.