I have a room similar in size to yours, just a little larger with many openings to other areas of the house. I have tried my M22s and they do a very admirable job and if that was all I could afford they would be fine by me. M60s are also a very fine choice with nice detailed sound. The M80s will give you all the extra little detail you could want from floostanding speaker, great midrange sound, low bass extension and the same highs as the rest of the Axiom line up as they all use the same tweeter.

I will second everything grunt said except I really like having my sub play below 20hz. In most cases if the sub is capable of playing below 20hz it is also capable of playing those higher frequencies with more authority, more SPL without straining, which equates to more shake and feel when required, just my opinion,YMMV.

I would recommend M80's and the VP180 or 160 initially, then add surrounds and finally a sub if you are going to have to piece this together, although you could add surrounds then the center, as a phantom center works very well unless you are listening off axis.