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)

Heaven Pierce Her - Hall of Sacreligious Remains (ULTRAKILL OST 6 - 1)

22 - Meganeko - The Cyber Grind

12 - Altars Of Apostasy (incl. "Hall Of Sacreligious Remains")

05 - Duel (Versus Reprise)

ULTRAKILL - [Deep Blue] But With EVEN MORE Extra Sax Parts by Rey Hunter

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

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

Heaven Pierce Her - War Without Reason (ULTRAKILL 7-4 Theme)

In Absentia ΛΟΓΟΣ (ULTRAKILL 8-1 Theme)

crawl

ULTRAKILL - Deep Blue (has Sax)

Neo