Like I said before: my GOG version work fine, except :
Music don't change if I go:
1) in the Blue Boar Inn
2) in the Dwarven Bread Inn
3) If I go over the bridge (where you the first time help soldiers fighting 2 Trolls) coming from Aleroth and going to the Farmlands, the music don't change, never.
Sometimes (or more often) if I go to the Dark Forest or Verdistis ... the music changed slower than by my disk version!
After going to the Wastelands all the music is okay, and that, makes me very happy !