I fixed this problem by installing the complete ALSA package (apt-get
install alsa), then it seems to work.
But now XMMS don't work anymore with latest ARTSD, but this is a known
problem and has nothing to do with PPC or Pegasos...
So I just disabled the ARTSD crap and XMMS uses the soundcard alone :)

Well but I didn't get the Soundblaster working, because it doesn't
seem to be in the kernel or available as kernel module for 2.6.4 ...
seems I have to compile it myself one day... but onboard sound works
good without ARTSD, so I will do that when I have too much time!