If you have room behind the listening position(say at least 4')for a rear sound field, you should use two back surround speakers in a 7.1 setup. Either discrete 7-channel material or applying a mode such as DPLIIx to 2 or 5 channel source material sends different "stereo" content to each of the two back speakers, for a better surround effect.

Enjoy the music, not the equipment.