Having the speakers on oppposite sides of the room will most likely create an odd sound as the M3's have a differnt sound characteristic than the M22's, especially if moving about in the room.
I would suggest to simply bump up the bass control on the receiver a couple DB and you will achieve the same exagerated upper bass level the M3 brings to the table.
An even better solution would be to get an EP400, or similar small sub, which reaches low enough to give full spectrum sound and small enough to fit anywhere. The fact this is for music only makes it a perfect fit for the 400 regardless of room size.
