You can disable audio channels (ssg0-2, fm0-5, whatever) using the Anex86 PC98 emulator (Anex86.exe -> Config -> Sound tab). Simply disable whatever channel suits your taste, then record using Audacity or a similar program. Should disabling the whole channels be a bit too much, you can edit the primary audio outputs (FM, SSG, PCM, Beep) and their wave forms under the wave tab (Anex86.exe -> Config -> Wave, adjust bars accordingly).
Also, Akyu's Untouched Score has all the PC98 music, so uploading that is probably a no-no. (ignoring everything I just said... Doo doo doo)