Unfortunately, some people with the Steam version reported this same issue, which Larian said after that release they would look into (as well as other reported problems). With a Divinity anthology (DD + BD + DKS) to be released later this month, presumably any fixes that are being made would be in before it went gold, so there may be a patch for the Steam version in the not too distant future (nothing officially confirmed). If that happens, Larian said they would release that updated version on GOG, as long as there are no issues in doing so.
There are no fixes for the music problem, that I know of, other than one person playing around adding disk version files to the Steam version of the game (
Music don't change if I go elswhere!).
