i have a yamaha receiver, and i like to run my music in 7-channel stereo, assuming i have more than the left/right mains hooked up at the time. this takes advantage of all the speakers while preserving the left-right separation that stereo provides. center channels get a mix of both sides. this, in my opinion, gives a more enveloping experience because the sound is then coming from all angles, instead of just the front.
CMT-340SE2 Mains & Center, CBM-170SE Surrounds, Rythmik F15, Emotiva XMC-1, Emotiva XPA-5