I was thinking it should be possible for the level music to be in .wav since it lets you use .wavs for the level intermission and main menu music. The dropdown menu only seems to allow MIDI though, so is it possible?
If you place specially name *.ogg files in a 'sndrsc' (NOT 'sndsrc', easy mistake) folder next to the exe, and uncheck 'use midi files' in the import sound, you can use non midi sound.
The naming convention is 1_1.ogg, where the first number is the pak number (usually 1) and the second number is the level, starting at 1.
Download mine: https://cptdrunkbear.itch.io/ancient-metal to see the folder, etc. if needed :D