What driver are you using? The SoundBlaster Live! 5.1 should use the emu10k1 module if I'm not mistaken. In command line, run as root:
lsmod
to see what modules you have loaded. If emu10k1 is loaded, then you're set. If not, run
modprobe emu10k1
then
lsmod
to make sure it loaded. Now, edit your /etc/resolv.conf file with your favorite text editor and add:
alias sound-slot-0 emu10k1
This should hopefully get your sound working. Hope this helps.