How long have you had the M2s? Before returning them -- if you have the time -- I'd try adjusting their placement in your room. When you've got them in the best possible position, allow yourself a week or so to listen to a lot of music just to get used to the sound.

If after all that you're still not satisfied, by all means upgrade to the M22s. I have a pair and they are absolutely awesome, but my room is only 12'x13'x8' -- and I have a nice SVS PB1-ISD to fill in the low end.