I recently went the opposite direction: sold my 5 channel Rotel amp and bought a couple of 2 channel amps (to use with another stereo amp that I already had). For my objectives (yours may be different), I chose to put the most money into the 2-channel section, and have been very happy that I did. I havent heard any higher end multi-channel amps, so I may be making an incorrect assumption here, but it seems to me that a HT amp will never do as well with music as a stereo amp; based on, if nothing else, power supply alone. Isnt that the rational behind having separates instead of a receiver and why some choose to go to mono-amps?
Your concerns about blending the center with the fronts could be alleviated the same way you're currently doing it: have the same brand amp running the center; or go with Russ advice and run the center in phantom mode.