I agree that the M80's wouldn't be your best choice for that room. M60's would be better. (Perhaps even M40's or M50's?)

Three QS series surrounds are your best bet for 6.1 as well. Like was previously stated, the M2i are rear fx speakers are great if in a pair. With the size of your room, and how close the surrounds will be to you, you could probably easily get away with the QS4's as well.

Good luck!