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