I've never resolved this. I say again, quite a mystery. I'm sure 3DGS can play music files in stereo. In fact it seems fairly sophisticated in that you can manipulate the files in various ways to create interesting effects and even create the sound to originate from entities within the level. I just can't believe stereo isn't an option.

All I know for sure at this point is that it can't be how I rendered the files, because as I said before if I play them in a program other than 3DGS I get to rock out to that stereo sound without any problem.