The sound effects work fine, but there's no music audio whatsoever(and it's turned on in the options).

Same problem here, on a Debian GNU/Linux: the sound effects play correctly, but not the music. No matter the settings.

I tried both the native Linux build of the game and the Windows build through WINE, on two different computers.

EDIT: I contacted GOG support about it, and will contact the game publisher and developer tomorrow.

EDIT 2: I contacted the game publisher, I’m going to give it a little time before I try reaching the game developer too.