Music must be in one of the following formats
	MOD		Amiga MOD format
	XM		eXtended Module (FastTracker 2)
	S3M		ScreamTracker 3
	IT		Impulse Tracker

To play them, you have to insert the file into the WAD file
you are loading. They have the same name as the MUS file would.

So, to replace Doom 1 E1M1, you would replace D_E1M1 with your
module file.

nxDoom will also load a music WAD file automatically, depending on
the game mode:
	Doom		DOOM1_XM.WAD
	Doom 2		DOOM2_XM.WAD
	TNT Evilution	TNT_XM.WAD
	Plutonia	PLUT_XM.WAD

It will add them after the Doom IWAD, and before any PWADs. Therefore,
you can replace music with your own. If there's no WAD file, it won't
try to load it. If it finds a MUS file in the WAD, it won't play.
