'Am new here, but I wanted to reiterate that my own problem was solved when I removed all drivers that were not being used from the directory that held the PSF driver [as Seifer Almasy first mentioned].
I also wanted to say that guests may not know how to specify the "midi = false" within Aali's driver. That is done by opening 'ff7_opengl.cfg' in notepad and changing the appropriate string there [then saving].
Anyway, after getting the PSF files to play, a new problem arose. The music wouldn't change when going into normal or boss battles. The fanfare celebration PSF triggered after a battle, and the scene music resumes, but the battle won't play [with Ramp/Stop either on or off and the appropriate PSF file names]. Eventually with some tinkering, I got it to play, but I am not sure how...if anyone has a similar problem later I can try to help.