Seems to be 3 audio assets used for for the music in 5-1. 'abyssalcavedrone', 'abyssalloopfastcalm', and 'abyssalloopfast'. All I have done is upload it to SC.

0:00 abyssalcavedrone (Drone Intro)
0:42 abyssalloopfastcalm (Calm Loop)
2:50 abyssalloopfast (Combat Loop)

enjoy the sax

devilmayquake.com

ULTRAKILL - Deep Blue (has Sax)

05 - Duel (Versus Reprise)

ULTRAKILL: DEEP BLUE

Deep Blue (Combat Loop)

Deep Blue

KEYGEN CHURCH - Tenebre Rosso Sangue (Calm)

I DO NOT OWN THIS

original by Keygen Church - https://youtu.be/KTCC053fLqs

Ultrakill is by Hakita

KEYGEN CHURCH - UltraChurch

ULTRAKILL Violence OST: Hear! The Siren Song Call of Death: Combat

Heaven Pierce Her - The World Looks Red (ULTRAKILL 7-1 Theme #2)

Heaven Pierce Her - Danse Macabre (ULTRAKILL 7-3 Theme #2)

Heaven Pierce Her - In Absentia ΛΟΓΟΣ (ULTRAKILL 8-1 Theme)

Morpher

ULTRAKILL - Deep Blue (has Sax)

Neo