Hi Autoboy,
Your room isn't that small; in fact, it's 2700 cu. ft, quite a bit larger than the "average" living room of 2100 cu. ft. Contrary to what Chesseroo said, in that size of room I would have recommended M60s unless there were real contraints on the physical size of the main speakers.
What you'll lose if you go with M2s is the ability to play very cleanly at very loud levels like the M60s can, simply because you'd be relying on the M2's one smallish woofer (two drivers) instead of the M60's dual woofers, separate midrange and tweeter--four drivers. This applies regardless of whether or not you are using a subwoofer, however, if much of your home theater and music playback is run in 5.1 with your sub, the peak demands on the M2s would be reduced, but limitations on peak power handling remain. In that sense, the M22s are a better choice because they use three drivers and have greater power handling and will play louder and cleaner in larger rooms.
Going to the M3s is certainly an option, but there is a slight lessening in midrange detail that is audible compared to the M60s, the M22s or the M2s.
As to the "sounding thin" comments, properly set up with a good subwoofer, the M2s or the M22s do NOT sound thin. Heard on their own with no sub, they have pleasant but not powerful bass that's useful to about 40 Hz. The M3 uses a larger woofer that produces a bump in the 100 Hz region which results in slightly more bass output and is a prudent choice when no subwoofer will be used.
Regards,
