Argh
I wrote summat about this a while back for a mate's UED pages. Let's see if I can remember.
Chizra1.umx, one section.
Section 0: Used in Chizra - Nali Water God (chizra.unr). Main level theme. Track loops.
Crater.umx, three sections.
Section 0: Used in Demon Crater (dcrater.unr). Main level theme. Track loops.
Section 1: Used in Demon Crater (dcrater.unr). Prolonged combat theme. Track loops.
Section 2: Unused. Short tension theme. Track leads into track 0.
DigSh.umx, three sections.
Section 0: Used in Rrajigar Mine (dig.unr) and Depths of Rrajigar (dug.unr). Main level theme. Track loops.
Section 1: Used in Rrajigar Mine (dig.unr). Skaarj ambush theme. Track loops.
Section 2: Used in Rrajigar Mine (dig.unr). Short level entry theme until Skaarj ambush. Track loops.
Dusk.umx, two sections.
Section 0: Used in NyLeve's Falls (nyleve.unr) and Sacred Passage (passage.unr). Main level theme. Track loops.
Section 1: Used in NyLeve's Falls (nyleve.unr) and Sacred Passage (passage.unr). Combat theme. Track loops.
EndEx.umx, two sections.
Section 0: Used in The Source Antechamber (extremeend.unr). Level intro theme. Track leads into section 1.
Section 1: Used in The Source Antechamber (extremeend.unr). Tumbling theme. Track loops.
EverSmoke.umx, two sections.
Section 0: Used in Bluff Eversmoking (bluff.unr). Main level theme. Track loops.
Section 1: Used in Bluff Eversmoking (bluff.unr). Dungeon theme. Track loops.
Fifth.umx, two sections.
Section 0: Used in The Trench (trench.unr). Main level theme. Track loops.
Section 1: Used in The Trench (trench.unr). Prolonged combat theme. Track loops.
FlyBy.ymx, one section.
Section 0: Used in Nali Castle flyby (unreal.unr). Main level theme. Track loops.
Fourth.umx, two sections.
Section 0: Used in Noork's Elbow (noork.unr). Main level theme. Track loops.
Section 1: Used in Noork's Elbow (noork.unr). Combat theme (long track only used briefly). Track loops.
Guardian.umx, one section.
Section 0: Used in Velora Pass (veloraend.unr). Titan theme. Track loops.
Hub2.umx, one section.
Section 0: Used in Harobed Village (harobed.unr). Main level theme. Track loops.
Section 1: Unused. Tension theme. Track loops.
Section 2: Used in Harobed Village (harobed.unr). Combat theme. Track loops.
Isotoxin.umx, one section.
Section 0: Used in Outpost 3J (skybase.unr). Main level theme. Track loops.
K_vision.umx, two sections.
Section 0: Used in Terraniux Underground (terralift.unr) and Terraniux (terraniux.unr). Main level theme. Track loops.
Section 1: Used in Terraniux Underground (terralift.unr) and Terraniux (terraniux.unr). Prolonged combat theme. Track loops.
Kran2.umx, two sections.
Section 0: Used in ISV-Kran Deck 1 (isvdeck1.unr). Main level theme. Track loops.
Section 1: Used in ISV-Kran Deck 1 (isvdeck1.unr). Prolonged combat theme. Track loops.
Kran32.umx (a.k.a. Kran3 in UnrealEd), two sections.
Section 0: Used in ISV-Kran Decks 3 and 2 (isvkran32.unr). Main level theme. Track loops.
Section 1: Used in ISV-Kran Decks 3 and 2 (isvkran32.unr). Prolonged combat theme. Track loops.
Nali.umx, three sections.
Section 0: Used in Dark Arena (dark.unr). Main level theme. Track loops.
Section 1: Used in Dark Arena (dark.unr). Titan combat theme. Track loops.
Newmca13.umx, two sections.
Section 0: Unused. Identical to Section 0 of EverSmoke.umx. Track loops.
Section 1: Unused. Tension theme based on Section 0. Track loops.
Newmca16.umx, one section.
Section 0: Unused. Level backing theme. Track loops.
Newmca7.umx, two sections.
Section 0: Used in Dasa Mountain Pass (dasapass.unr) and Cellars at Dasa Pass (dasacellars.unr). Main level theme. Track loops.
Section 1: Used in Cellars at Dasa Pass (dasacellars.unr). Prolonged combat theme. Track loops.
Newmca9.umx, two sections.
Section 0: Used in ISV-Kran Deck 4 (isvkran4.unr). Main level theme. Track loops.
Section 1: Used in ISV-Kran Deck 4 (isvkran4.unr). Prolonged combat theme. Track loops.
Opal.umx, one section.
Section 0: Unused. Short tension theme. Track loops.
QueenSong.umx, three sections.
Section 0: Used in The Source (queenend.unr). Main level theme. Track loops.
Section 1: Unused. Tension theme. Track loops.
Section 2: Used in The Source (queenend.unr). Queen combat theme. Track loops.
Seti.umx, two sections.
Section 0: Used in The Ceremonial Chambers (ceremony.unr). Main level theme. Track loops.
Section 1: Unused. Tension theme. Track loops.
SkyTwn.umx, two sections.
Section 0: Used in Na Pali Haven (skytown.unr). Main level theme. Track loops.
Section 1: Used in Na Pali Haven (skytown.unr). Combat theme. Track loops.
Spire.umx, three sections.
Section 0: Used in Spire Village (spirevillage.unr) and The Sunspire (thesunspire.unr). Main level theme. Track loops.
Section 1: Unused. Quiet tension theme. Track loops.
Section 2: Used in The Sunspire (thesunspire.unr). Main level theme #2 (inside the Sunspire). Track loops.
Surface.umx, one section.
Section 0: Used in Gateway to Na Pali (skycaves.unr). Main level theme. Track loops.
Unreal4.umx, three sections.
Section 0: Used in MotherShip Lab (extremelab.unr), MotherShip Core (extremecore.unr), Skaarj Generator (extremegen.unr) and The Darkening (extremedark.unr). Main level theme. Track loops.
Section 1: Used in MotherShip Lab (extremelab.unr), MotherShip Core (extremecore.unr), Skaarj Generator (extremegen.unr) and The Darkening (extremedark.unr). Prolonged combat theme. Track loops.
Section 2: Used in The Darkening (extremedark.unr). Short combat theme. Track leads into Section 1.
UTemple.umx, two sections.
Section 0: Used in Temple of Vandora (ruins.unr). Main level theme. Track loops.
Section 1: Used in Temple of Vandora (ruins.unr). Combat theme. Track loops.
utend.umx, one section.
Section 0: Used in Ending Sequence (endgame.unr). Main level theme. Track loops.
Vortex.umx, two sections.
Section 0: Used in Vortex Rikers (vortex2.unr). Main level theme. Track loops.
Section 1: Used in Vortex Rikers (vortex2.unr). Repeated heartbeat sound. Track loops.
WarGate.umx, three sections.
Section 0: Used in Serpent Canyon (naliboat.unr), Nali Castle (nalic.unr) and DemonLord's Lair (nalilord.unr). Main level theme. Track loops.
Section 1: Used in Nali Castle (nalic.unr). Prolonged combat theme. Track loops.
Section 2: Used in Serpent Canyon (naliboat.unr). Cave & windmill theme. Track loops.
Warlord.umx, one section.
Section 0: Used in DemonLord's Lair (nalilord.unr) and Skaarj Generator (extremegen.unr). Warlord combat theme. Track loops.
Maps MotherShip Basement (extremebeg.unr), Illumination (extremedgen.unr), entry.unr, gateway.unr, dknightop.unr and dm*.unr have no music.
Tracks flyby.umx, nali.umx, hub2.umx, wargate.umx, opal.umx, spire.umx, utemple.umx and endex.umx are also used in Return to Na Pali (along with several new tracks).
Info on the new Na Pali tracks can be provided on request.
Hope that helps