Sorry this isn't technically romhacking but I figured someone here might have knowledge on the topic.
I've managed to figure out how to do this with PS1 music files (find the .psf files containing the music, use a program called psfisolate which breaks the .psf file down into .minipsf files, each containing one instrument of the entire track)
However, not only have I found no such program that works with .psf2 files, but the archives of PS2 music rips I have found have downloads of files that are not .psf2 files. For instance, Legaia 2's download came with .leg files and MegaMan X Command Mission came with .adx files. I was able to play these files through vgmstream in foobar, and therefore can convert to WAV,
but I'm looking to be able to do as I said above, have a separate file for each instrument data. I don't understand all of this fully, so it might not be possible with the way the PS2 reads/stores audio, but I did see mention of .minipsf2 files on the Video Game Music Preservation Wiki, which is giving me hope that it is indeed possible.
Thank you for reading!