Your wife is overly sensitive to the exposed speakers. She really won't notice them much. Mine complained, but we weren't married yet so she really couldn't mount too big of a battle. She's forgotten about it and enjoys them now.
The 175 sub will be worthless with the M80s in there, especially in that BIG of a room. You'll want to look at subs that are small yet powerful. The only powerful subs that Axiom makes are the 350 and up. With a room as big as your's, you'll need a truely massive sub in order to really fill it with tactile bass. Their smaller subs are for small rooms and pairs with their small speakers. That said, the M80s should fill it with enough bass to be very enjoyable on their own. You'll miss out on the tactile, pounding bass that wakes up your house.
I'm not sure a truely hard hitting low end is appropriate in an open great room. Look at all those open doorways. It's a sure way to get yelled at by the wife.
The rear speaker placement is really far back. I don't think you will get much stereo separation back there from 2 m2's. You could go single vp100 back there but either will be fine IMO.
