are you running windows xp?
i have mine set to 5.1 surround sound in the sound settings and it always runs 4 speakers unless its a 5.1 game/movie then its in 5.1
i had a bit of trouble playing mp3 in 4 speaker with winamp, it would only play 2 speakers, but if you go into the preferences you can change it to hardware acceleration and that forces it into 4 speakers