Updated:
http://wiki.qhimm.com/view/FF7/Field/Script/Opcodes/F2_AKAOC8 Set music pan? (noop in PC version)
C9 Music pan transition? (noop in PC version)
CA Music pan fade? (noop in PC version)
These appear to be totally unused in PSX version also. If you can do a quick scan of the script for me, and let me know any areas that use one of these, I will test it again. But it does look like these are simply not used in any version. I also don't recall ANY part of the game where the music balance changes. Only the sound effect channels do this.
Also, from what I can see, only TWO operations actually makes use of parameter 1,2 and 3. Operation C2 Music volume fade, and Operation D2, Music tempo fade.
. All the rest make use of just 2 input parameters. Parameter 1: Time for fade, where TimeForFadeInSeconds = Param1 / 60.
Parameter 2: Starting Volume
Parameter 3: Ending Volume
In other words, C2 is actually just setting an initial volume - then doing a transition to an ending volume. It wasn't needed, since the programmers could do this in two steps using C0 and C1. C2 is therefore just a faster way of doing C0 + C1.
"Fade" is the wrong word to use, too. It's more of a "From-To Volume Transition" / "From-To tempo transition"