Otto, I agree that if a given disc has been expertly recorded, perfectly mixed with channels balanced and correctly mastered, little (if any) tweaking is needed. I own hundreds of hi-rez titles and the majority of those do not IMHO fall into the 'perfect sound' category.
Also, I have many great sounding multichannel upmixes and transfers by DKA, AoQ, Holland123, Sansdancer, Floydflush, XTC343, Juande, Romanotrax and others. Each of these engineers approach the channel balances in their own way - some with very aggressive rear channels, others with pronounced or suppressed center channel, and we all know that no two people agree on what should be going on in the LFE. I feed all my multi-channel sources into a central Sony 5.1/7.1 preamp/amp that then feeds separate stereo amps for my front and rear channels and a stereo power amp for the subwoofers. The Sony amp powers the center and overhead (channels 6&7) speakers. Once I have the channel balance set to my liking on the F,R&SW amps, I can control the volume of the entire system using the Sony amp's control. I love the flexibility this set-up affords me.