Yeah to do HT right, you gotta do a center. If you like no center for your mulit channel music or whatever, or stereo needs, than click off the center! it's that easy. For movies, you simply must do the center thing for off axis listening with multiple seats!...it's just better(I mean the movie mixers/engineers desgigned it that way..duh!)
I am also an avid 2 channel guy(infact my ht has been 2 ch w/sub for years, but then it's just me listening!..no one else. Still, dedicated HT systems for the whole familiy NEED A CENTER CHANNEL!..end of discussion.
To your question, the 2 channel amp(or even mono's) will outperform(all things equal) multi channel amps in the same brand, most every time! YOu might consider 2 channel high end amp like Pass X250 for the 3.6's(which will handle the 3.6 and mate well) and add 3/5 channel amps (like the sonically similar, if less refined ultimately, ATI amps!) for the rest. ATI makes an excellently clear, neutral, musical and extended multi channel, that's very strong, bullet proof, and high end! It's not as good as many high end amp totally, but then you're talking HT. Still, it holds it's own, has the clarity, neutrality of say the Pass, krell, MCCormmack, and similarly balanced sounding/neutral amps, but is strong class B indeed, not A.
Anyway, for the money, this is a no-loose option.
I've sold the Thiels on a retail level, and owned the 1.5's and 2.3's for years. The Pass is world class, and mateches the 3.6's, and the ATI's are a perfect fit for the rest!..without UNECESSARITY breaking the bank.
Hope this helps