i have a santa cruz too, and it was a pain to get working, until i found out how, and then it was easy. 😛
anyways, for simultaneous sounds you need something like ESD (enlightenment sound daemon), which is supposed to let you do that, but after messing with it for a bit, it still wasnt working so i just said screw it. the only time i have 2 sounds going at once is when i wanna watch a video or some flash or something, and at those times i dont want my music going anyways.
for the 4 speakers, i have no clue, as i use a pair of 22 dollar labtec speakers 🙁
and just by chance, does your sound randomly go to crap? i mean, one song will stop playing, then the next will start, and its all crappy sounding, like its being played at a really low sample rate like 11khz or even lower. and the sound stays like that until i fix it. to fix it i wrote a little script to remove and then insert all of the modules again. it looks like this:
#!/bin/sh
sudo modprobe -r cs46xx
sudo modprobe -r ac97_codec
sudo modprobe -r soundcore
sudo modprobe soundcore
sudo modprobe ac97_codec
sudo modprobe cs46xx
sudo aumix -v 87
sudo aumix -w 78
echo "sound fixed sucka!"
exit 0
i just assigned that to a key binding, so its not too bad anymore. i just stop my mp3, hit alt+shift+F, wait a second, and then start my music again. really wierd though, do you have the same problem?