Welcome Paul,
I have 4,000 cubic feet (see Wall of Fame for pictures) with the Epic80-600 system. I considered in-walls but realized that I would be giving up too much in terms of sound quality. There are two major problems with in-walls: 1. diffraction effects and 2. inability to tweak their location and angle. This coupled with worse frequency response than floor-standers puts you at a disadvantage before you're even out of the gates.
Go with M80s, 4xQS8s, VP150 and EP600 and never look back. If you're strapped for cash, forego 2 of the QS8s and the VP150...you can always add them later. But don't miss out on the EP600 especially if you watch movies!
I have no doubt that you will enjoy your Axioms. Whatever floor-standers you end up buying, make an equilateral triangle with them and your listening position, toe them in, keep them away from side walls, move them a couple of feet out from the front wall and try to keep the area between them open. Sound treat the ceiling and floor area that is in between you and the speakers and you will be a happy camper. Bass traps in the corners may be a good idea too. Good luck!
