From what I understand, it works somewhat like a music production DAW. You can create as many sounds as you like. If you assigned a bunch to the music volume channel & then started them at the same time I believe you could use Lua or action parts (if available) to fade in/out active sounds as needed. I like dynamic music in games - always fun to listen to; especially if it changes dynamically based on what you are currently doing like the music in the game Mark of the Ninja
a process interview type thing of how they approached the dynamic background music design for the game I just mentioned. It's an interesting read, I guess & possibly something that someone might be able to get a few ideas from.
The simplest method would be to have a single track with each instrument/audio track from the song exported individually, you can them import each & start them all playing at the same time so that you can fade in/out parts as you need them.
Broken Sword dynamic sound approach was much simpler as they used music cues that were triggered by the protagonists actions/animations.
@Lebostein: you should be able to assign each sound to a specific volume channel. Sound, Music, Voice, etc. Then the global volume will control the general volume level for the sound, but you will then be able affect the volume for each individual sound too I believe.