Strong vote for M2's as rears. My understanding is that the rear channel info is meant to be for direct radiators. In addition, 5.1 channel music on SACD and DVD-A sounds much better when the surround channels come from direct radiating speakers located behind the listening position. I've tried it both ways, and surrounds to the rear from direct speakers won by a mile. One caveat...make sure your receiver or pre/pro has a full set of 7.1 inputs so you can plug the surround channels from your DVD-A/SACD player into the rear channels of your receiver, or that there is some other way of making sure that the surround channels can be sent to the rear speakers in the multichannel input mode.
Mark
