We did a similar thing with System Shock 2 for ambient sounds/music. We had zone triggers which fed into a DSL for queuing up/randomizing/looping audio segments. I built the runtime on top of an existing virtual-machine style audio playback system which had been developed for flight sims, where it was used to stitch together voices for ground control. I was a fairly junior dev at the time, and IIRC I was not able to implement the requested cross-fading feature in time to ship. Fortunately, the silence between tracks worked pretty well with the desired atmospheric effect.