From MEPIS Documentation Wiki
If you are running a Windows/MEPIS dual-boot system and your soundcard is a Soundblaster Extigy (USB soundcard), you may find that although the Extigy works perfectly well in MEPIS it will stop working in Windows. Even reloading the drivers in Windows may have no effect. It's tempting to blame Windows for this problem, as so many problems actually are Windows fault. But in this case Windows is blameless.
The problem is that during the shutdown process MEPIS is sending a STOP message to the soundcard. Windows is unable to restart the card during boot-up (OK - technically that is Windows fault), although MEPIS has no difficulty doing so. Thus you get sound in MEPIS and silence in Windows.
This is the solution that I've found:
1. In Synaptic, find KSysV and install it.
2. Run ksysv (the menu item is "System > SysV-Init Editor", or just type "ksysv" in "Run Command...").
3. On the far right-hand side of the screen are the Runlevel 6 START and STOP boxes (START is on top, STOP is underneath it).
4. In the Runlevel 6 STOP box, click on "alsa" to highlight it, then remove it (click on "Cut").
5. Save your changes (ksysv will pop some scary warning messages up on the screen about how incorrect changes here can lock your computer up on boot - if the only thing you've changed is what I've detailed above, you'll be fine).
That's it. MEPIS will no longer send a STOP message to the Extigy when you are shutting down. The side-effect appears to be that each time you start MEPIS the volume level in the mixer will be at a default setting instead of a saved setting. Just push it up a coupla ticks and you're good to go.
Hey! Extigy sound is all scratchy in MEPIS...
For some reason, alsa doesn't like the Extigy. Sure, it'll play sound, but the sound quality isn't very good, and everything sounds like it's being played on a very dusty vinyl LP.
Solution: go into Control Center, click on "Sound and Multimedia", then on "Sound System". Click on the Hardware tab. Click on the "Select the audio device" dropdown and change it from "Autodetect" to either "Open Sound System" or "Threaded Open Sound System" (I honestly don't know the difference between the two, but I've tried both and they both seem to work equally well) (Note from mos: Threaded means its able to handle multiple sound streams and is more capable of realtime playback. Generally you may want threaded.) At the bottom of the screen click on the "Apply" button.
Play an mp3. You'll notice an immediate and vast improvement in the sound quality - no more pops and scratches.