Konami were very late with delivering their (MTS?) system that was their audio/tasking thing, we were not given anything in advance. As such we've just found in the code where the samples and music had to be played, and as I've said above we "stole" (downloaded) the music data from the web-sites that had them (not sure how they've got all the effects, or it could be that we also found some waveforms in the source package).
I think at some point the "radio-codec" (okay, that's the actual Radio that Snake talks to the others) used this system - maybe a bit like fibers/threads, when a message comes, then switches. I'm not sure what exactly I did, and how much I understood it well (threads/fibers were not my thing back then... that much) but we've got it working.