Oddly enough, after a little fiddling, I arrived at the same point - set it to 7.1 w/no 'side' speakers... Also, the more options (like Dolby) that you enable, the more likely that you'll have audio 'stutter' problems in WMC - disable everything possible, and it sounds fine! Another oddity that I've noticed is that in WMC under Vista x86, the sound seems 'biased' to the front speaker triplet, as I'd prefer; under x64, they seem 'biased' toward the rear, so I leave it selected to two channel - can always adjust for actual 5.1/7.1 encoded on DVDs.