the wife responses are awesome.
.. and I thought svs subs were beasts. They pale in comparison to yours. Is there room in the back wall for those new subs? If they do fit, what's to stop them from blowing the velvet like a curtain in the wind? (i'm not entirely kidding... have you ever seen those videos where the air moving through the ports of large subs can blow out a row full of candles ? ) Also are you keeping the smaller subs in the back wall? They might be better served the the back corners of the room if they fit rather than on top of the other speakers. (not that you need them)
Also i was talking to an installer, he strongly recommended if doing a false wall behind the screen, to treat the back of wall behind the screen with sound absorbing material so you dont get odd reflections.