Hi mike. I have and love my M22 and M2 speakers but if you really want more mid bass then rather than doubling up on the M22s as mains I would go with M80s which have one hell of a mid bass punch. In fact their tight bass and mid bass punch was one of the two things that made me choose them over Focal, Paradigm and B&W speakers I was also looking at.
In my apartment I tried out dual over and under M22s with my M80 mains and it sounded great. There was a drop in the mid bass coming from the center in this configuration compared to running an M80 center. I think that’s because most sound engineers know that people just don’t usually have full range speakers as centers so they master their recordings accordingly. I actually found the missing center mid bass was more noticeable with movies than music. I posted some of my impressions in this thread:http://www.axiomaudio.com/boards/ubbthre...true#Post218171
Note that the farther away you sit from your front speakers the less noticeable the difference in mid bass is between speakers because the mid bass drops off very quickly with distance especially in a room where reflections start to interfere with the mid bass directionality.
Another thing to consider is a mid bass module:http://www.hsuresearch.com/products/mbm-12mk2.html
I’ve been trying to talk myself into trying one.