So I'm working on the Watery Pass in TfW and I stumbled upon some info that, as far as I know, hasn't been documented yet.
Ever notice that when you enter the Waterfall on the way to Octomamm, that first screen (before jumping down the waterfall) doesn't have music, but just a running water sound?
Turns out, the "music" byte for that map is set at 44. But, songs in FFIV are only numbered up to 37. So I isolated this byte and did some experimenting. Here's what I came up with...
38 through 3D - NOTHING
3E - PROPELLER SOUND (FADES IN)
3F - THREE GONGS, SHIP WHISTLE BLOWS (I THINK WHEN THE SHIP TAKES OFF FROM FABUL)
40 - A DISTANT CRASH SOUND
41 - A NOT-SO-DISTANT CRASH SOUND
42 - EARTHQUAKE
43 - PROLONGED FALLING SOUND (PERHAPS USED WHEN CID BOMBS THE ENTRANCE TO THE UNDERWORLD?)
44 - RUSHING WATER (WATERFALL)
45 - NOTHING
46 (and above?) - CRASHES GAME
Not a whole lot of useful stuff here, but maybe someone will be interested.
FF4kster doesn't have the ability to set these bytes above the last song (Ending 3), so you'd have to isolate and change the byte manually. For a shortcut to doing this, set an Execute breakpoint to 00/83EF, then enter the location whose music you want to change. 83EF will execute 12 (0C) times. You'll see the Y register increment by 1 each time. When Y = 0007, the byte being read is your music byte.
I imagine these sound effect "songs" can be called via event instructions, too, but doing so would likewise be impossible with FF4kster. Describing a similar shortcut to manually change these would be a bit more difficult, too, because of the way the game loads event instructions.