Hello, I have two linux distributions (Slackware 10.1 and Ubuntu Edgy 10.6) and on both I have the same problem. When I try to play music with xmms at a higher volume, the sound becomes unclear. It isn't my sound card's problem or something, on windows it works fine, and on linux i have the same problem on both my old and my new audio system. Also, my subwoofer doesn't work at all. I installed w32codecs for Ubuntu and i have the same problem. I'm using alsa as the output plugin. If i lower the PCM volume and raise the volume from the sound system it seems I have the clarity back, but can't have the volume as high as my sound system supports. Also, I need some way to make the subwoofer work too.
Any help is appreciated.
Sorry for my bad english.

Edit: I have a 5.1 audio system. I have installed all alsa drivers with "sudo apt-get install alsa-base alsa-utils alsa-oss alsa-tools alsa-tools-gui" on ubuntu and also w3codecs. Only 2 of the loudspeakers work, the rest of four of them are not outputting anything. Isn't there any way I can "tell" my system I have a 5.1 surround audio system? Or what else can I do to make all of them work and without losing quality at a higher volume ?

Second edit: I've found someone else with a problem exactly as mine on http://ubuntuforums.org/showthread.php?p=2212562, he has the same sound card i have (nForce3 AC'97) and he has the same problem I have, but noone answered him.