There was a topic posted here about this issue before by someone else, and it was determined that the reason Gabriel Knight hung/stalled the Sound Canvas upon exiting the game was because Sierra hardcoded a command to send to the MIDI port that was incompatible with the way the ESS Audiodrive operated. I don't recall a solution to this issue being discussed, but if there is one, I'd like to hear it. It's awfully annoying to have to do a complete shut down/reboot of DOS just to get my Roland working again. The rest of the system will still run, but only with Sound Blaster capability until said reboot is performed. Gabriel Knight is the only game that does this, and is the only SIERRA game that does this.

Note: Sometimes exiting the game leaves an annoying hanging note if you exit in the wrong part of the song.