I own Montana SPIIs. The best (music) amps I've heard on them are my Pass Aleph 2s, or my Pass Aleph 60s.
The soft dome tweeters need a detailed amp to sound their best - in my opinion.
I've used these amps with the Adcom GFP 750, Aleph P, and Pass X1 preamps.
My room is the same size as yours. I haven't clipped either amp, but I don't listen really loud......