Hi,
I'd suggest trying an 80-Hz crossover frequency for the M2s and your subwoofer and see how it sounds. The M2's bass response is quite strong and smooth down to 70 Hz, as you can see from these NRC anechoic frequency response curves:
http://www.soundstagenetwork.com/measurements/axiom_m2i/ To your first question, while I'd acknowledge that every room is different, if you have a reasonable mix of both reflective and absorptive surfaces--carpet or area rugs, some upholstered furniture, some bookshelves or objects on the side walls to just break up the reflections a bit (not absorb them)-- there's an excellent chance that you don't need any room treatments. You certainly don't want to overtreat a room so that it ends up being quite dead. I've heard some "professionally" treated rooms that were so dead it was like listening on headphones. Very peculiar, with the surround signals appearing in the middle of my head because there were no natural reflections taking place in the room near and around the surround speakers.
Alan
