My personal opinion....strictly based upon anecdotal postings here... is that two 175s still won't approach the capabilities of one 500. Two 350s might have a shot at it, though.
Again, my opinion only is that your current sub is maybe being localized because it's outputting higher frequencies. If you were able to shift the crossover point lower so the sub is only outputting the lower end of the bass spectrum, and not the mid bass, localization would be less of a problem.
To me, this is the concern of using M22s in a big room. They may go loud enough, but they can't put out enough bass to take ANY duty away from a sub... they are absolutely reliant upon that sub (especially for movies).
BTW- when I say that this is anecdotal, I mean it: I've never heard the 22s, the 175, the current 350 or the 500. Seriously, it's all just theory.
