I just tried the game on a 5.1 system and I noticed it doesn't really matter what sound mix I choose: mono-stereo-surround, the sound will be the same. :S
Feels like all the main sounds came from the Center - when no music at all other speakers silent! - and the music from the Left-Right.

I have: Win7 32 bit, ASUS Xonar DSX sound card.

I just don't know the game sound that badly designed or my rig doesn't compatible with the game.