So for some reason CD-Music is not enabled by Default in C7 here are the steps to enable it (its likely that Ziggurat forgot to set it up in the games setup program as its all properly configured in DosBox)
[Please note that I already have set up CD Music in my copy of the game so it may look different but if your setup says "Adlib music" follow the instructions below:

1. When you start up the game using the GOG provided shortcut (Fig-1) you are provided with a list of options, please select "Run Setup".

2. When you are in the Setup program proper use the Arrow keys to navigate to "MUSIC configuration" (Fig-2) and hit Enter.

3. Select "CD Music" (Fig-3) and press Enter again.

4. Hit F10 or Esc, Save your configuration and quit.

5. Start the game and you should now have CD music.

Some Notes about CD music:

1. There are only 4 actual music tracks the others are just blanks, this is not a problem with the gog release, this is
part of the original CD release as well.
2. You can access a CD music track control in the "adjust audio" (Fig-5)
Just select the function you want and hit space sometimes the skip function doesn't work as well, but that's because of the blank tracks, need to do more research.