Both the M22 and M40 are great buys, depending on musical tastes. If you are really into pop recordings, the laid-back sound of the M40 will actually be a plus rather than a shortcoming of the speaker. Technically, tonal matching on movie effects will be better with the M22, but this is really a minute issue outside of a professional review.
If I could risk opening up ye olde can of worms about bothering with 6.1, why not upgrade the choice of QS4s in the back to a single pair of QS8s, then see if you feel the need to bother with surround backs?
