Personally I do not think there is enough seperation from side surrounds to the rear channels even if the sides are pushed ahead a foot or so. The effects with direct radiating speakers are still going to feel like they are coming from the sides and not from behind as intended, not much added to the experience for the cost of 2 more speakers and wiring, IMO. I would do away with 7.1 and stick with 5.1 with the side surrounds in the present location.
Pushing smaller speakers to equal the output of larger speakers could strain them and make them sound bad as they are not designed to push loudness levels, not the I think there will be a problem with M2/M0 scenario, just pointing out that pushing a smaller speaker to levels it can't reach due to physical constraints causes bad things to happen. I have not heard the M0's so I can not really say what the marriage of M2/M0 will sound like.
I suspect we have WAF involved in this situation.