This is more a remain­der for me: in order to make the sur­round work for mp3s with the CA0106 driver with alsa (for me it’s a Sound Blaster Live! 24 bit), here’s the .asoundrc that should be used:

pcm.!dmix {
   type plug
   slave {
       pcm surround51
       channels 6
   }
}
pcm.!default {
   type plug
   slave.pcm "dmix"
   slave.channels 6
   route_policy duplicate
}