I had the same problem too, but it turns out you don't need to add additional commas in volume, loopstart and loopend.
insert your stage into the extrastages section in your select.def file like this:
stages/example.def, music=sound/example.ogg 100 0 0the 1st number is for volume
the 2nd number is the loopstart point
and the 3rd number is the loopend point
hopefully this'll help.