Just use the same sound drive the demo uses with your other SCI games. Just open up resoruce.cfg from the demo, then get the sound driver out of it I think it is this one:
soundDrv = STD.DRV
Then past it over the soundDrv = *** in your other SCI games resource.cfg file. This will make it so it will use the same sound driver as the one from the demo. Then you should be able to hear the sound.