| posts: 205 | Location: Finland
Any game setting for audio channels (stereo or multichannel) should take precedence over the Windows setting. Try changing the game setting.
It's conceivable that having multichannel setting in-game and stereo in Windows may screw up the audio path in that it may strip all channels except left and right front. Try the same setting in both game and Windows.
Another thing that may mangle the audio is if you have a stereo source (or Windows strips all but the stereo channels) but have virtual 3D sound enabled in your sound card.