The way I understand it, the platforms/games normally refer to the album (music) itself, not how it was packaged/obtained.
If like Hellacia says the PSX FF ports sound a bit different, but this album sounds only like the Snes version, platform = Snes (ie.- 'you can't hear the PSX versions here').
Ie.- this
FF Box includes music from the GBA versions of FF4-6. The Snes music may be the original, but what you hear there is GBA audio only, so the platform is just GBA.
In cases when the audio is identical (exact ports/emulations) you could include several platforms, but I personally think it's better to add only the original source platform. Otherwise you'd be adding Wii/Virtual Console and whatnot for every OST.
Hope that makes some sense.