After two days of listening to my M60s I realized I needed a sub. Your room dimensions are similar to mine. I spent an entire weekend locating the sub in various locations and found that up front next to a main was the best home for it. A corner location was too boomy at times. I considered the M22s but worried about them being too small, and the fact that I like my music loud. 75% of my listening is 2.1 channel stereo (with the sub). I'm really happy I chose the M60s. Because I was tight on space, I chose a small-form sub solution from a different company, the SB12-Plus from SVS. It's proven to be an excellent match for the M60s. If you have an open adjoining room, keep the sub three or four feet away from the corner where the two rooms adjoin.
As was mentioned here, calibration is critical, and be certain to set your mains to small.
