In terms of "breathing space for the ports" you should be fine. The only other issue with speaker-to-wall distance is the overall bass reinforcement thing, which is more of a "distance to corner" than "distance to wall".

How far are the M3s going to be from the side walls ? If more than a couple of feet then "no problem".

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8