Fascinating. That could explain some things about why its so hard to extract or pin down the PSX-MIDI data in a PSX game in comparison to doing so in an SNES game.
You know how, on some PSX games that use XA audio, all the songs are compiled into one master XA file, and the PSX SPU simply cuts to the correct point in the track to play the requested song? Well, something similar to that could be happening with the PSX samples, the SPU could simply be jumping to the requested sample points in the file and loading them dynamically into the SPU RAM.
Did anybody get that?