More channels than four seems to me like the manufacturers’ pushing 1080p TVs to those that already owned 720p with screen sizes 50" and under. If you sit the proper distance from the two different resolution 50" TVs of the same quality otherwise, you will not see any improvement in the picture unless the you have eyesight like an eagle.
The 1080’s improved resolution is visible with 60" and larger TVs, but they put crappy motion processors in the standard (affordable) TVs to meet competitive average-consumer price points so you live with a picture with higher-definition motion slur ( the worst) unless you buy the best. The old Panasonic 720p plasma’s kill the newer 1080p sets for blacks, depth, and natural picture rendition unless you go to the ultra-expensive Oled sets. Same with multi-channel audio vs 2 channel IMO.
I sold my Martin Logan Stage center channel speaker and mono Marantz MA700 center channel amp after trying just my two-channel system with my processor in "phantom center" mode along with 2 rear channels. The continuity of motion, tone, and height is much better to my ears. Much more realistic sound in every way than trying to integrate a center channel above or below my screen.
I run the L/R out of the processor to my hi-end 2-channel preamp’s balanced inputs via long XLR ICs and set the preamp’s volume at unity gain, so those two channels get the best possible source quality. Of course, the processor is not in the loop for two-channel music listening, which is 99% of the time for me. I confess that when I do use the processor for movies or multi-channel music, I set the processor to "Pure Audio" mode, bypassing the Audyssey room correction and any other circuitry possible inside the processor. Possible and preferable because my room and my 2-channel rig are right.
Best to you gdhal,
Dave