You can create an unlimited number of playlists when you subscribe to a music plan through ShootProof. You'll add songs to each playlist, and then assign a playlist to each gallery.
To assign a playlist to a gallery:
1. Go to Photos > Galleries
2. Click on the specific gallery to which you'd like to add music
3. Go to Gallery Settings > Gallery
4. Activate "Add music playlist"
5. Choose a Playlist, and save!