I got very similar problemI have a 5.1 Sound System. My motherboard has an integrated nvidia 2 sound card, it supports 5.1 configuration. In nvidia mixer when I use sound test I can't hear the subwooofer working. And when I try to watch movies, not all music and sounds (usually voices) I can hear with 5.1 sound system. But when I choose 4 chanels system everything is OK exept that my subwooofer is useless. Well.... It appears not with all movies. Some formats run perfect with 5.1 system.That problem appeared when I reinstalled my Windows XP. I got newest drivers, but nothing changed. Thank you for your help in advance.--Justinas