Also, for best comaptibility, you should instead make a new lump with your music.
To do this you can just import an OGG (or some other music file) into the WAD, name it O_XXXXXX (with the Xs being anything), then go to your level header, and add a new line that says:
"Music = XXXXXX" (The Xs are the same characters as the ones you named the OGG with, also no quotation)
For MIDI files, you need to name them D_XXXXXX instead of O_XXXXXX.
EDIT: Also i forgot to mention your song names can be any length from 1 character to 6 characters.