When the "Rebirth" setting for Soundtrack is turned on:

• Downpour, Mines, Mausoleum, Corpse, Planetariums, Alt Path Boss Theme, Witness theme, and the alt path Calm (twisted too)
  
• now use their tracks from Repentance.
  

When the "Remix" setting for Soundtrack is turned on:

• Catacombs, Necropolis, Boss Fight, Mom, Satan, ???, The Lamb, Devil Room, and Angel Rooms now use their Antibirth theme
  

• Cellar, Downpour, Caves, Catacombs, Mines, Depths, Necropolis, Womb, Corpse, Sheol, and Dark Room now have layers composed by LuFeDiRo
  

Credits:
Mudeth: Composed the Antibirth soundtrack
Ridiculon: Composed the base game soundtrack
Rick: made the Rebirth unpacker
LuFeDiRo: made those awesome layers for the Antibirth tracks

Link for people who don't wanna sign in: Right here


Also check out Repackance for Rebirth!