Unused Music[]
Track #10 on the NSF is an unused song. The official soundtrack album includes an arranged version of this song called "Sheltem's Theme". This would seem to suggest the song was intended to be used in Sheltem's Maze (aka The Soul Maze), but the normal Astral Plane music got used there instead.
Source: [FlyingOmelette]
NSF Source: [Zophar.net]
Soundtrack Source: [Square Enix Music Online]