Why not try the m22's as rear surrounds. On the audioholics website I remember a review where the guy used your same setup and m80's for rear surrounds. He though it was a great way to set them up. Link:

http://www.audioholics.com/reviews/speakers/floorstanding/axiom-audio-epic-80-600/page-5
You might be able to get a similar effect if your room is large enough.

- Nick