In \SOUND\ all the instrument data is kept. The actual midi sequences are in the PS1 SEQ format. There locations are a bit of a mystery however.
I would not broach the sound for a bit, it will take a bit more research. However the FIELD 3d information (IE characters), I'm playing with right now, so maybe that will keep you ocupied for a bit? I suggest for sound implement a stub. Sound is more difficult than the graphic information by far. The midi sequences are played by a specific yamaha synth. (The PS1 GPU) I believe this is where one will need to borrow from a playstation emulator's GPU code to make the synth. Sound will need to be in a seperate thread likely. To play the PC version of sound, well I suppose just feed the midi sequences to the synth (non SEQ format).
It's possible on the PS1 the music is compressed, in fact it's very likely. Midi data compresses quite well (ussually 8:1).
Cyb