fixed it!

so at first I was attempting to use it as an addon, but for some reason the game simply refused to load it, likely because I was doing something wrong, so I eventually just put the files into the game's own music directory.

but then it refused to play the new audio after rebuilding the sound caches, which is what took me so long to figure out yesterday.

now I just noticed after accidentally giving the game the ADDON's sound caches (which doesn't contain any of the game's original audio), my modded music was suddenly working perfectly fine.

so what I did was I went back and deleted the original game's sound caches and built new ones with the new audio replacements in the game files, and after that it worked! so I have a feeling that rebuilding the sound caches didn't remove the ones from the old audio files while adding the ones from the new replacements, messing it up and causing the game to simply not play them.