The shareware (demo) version of the game is the only version that uses
MIDI.

The registered version of the game was distributed on CD, and played
the music from audio tracks on the disc. This isn't supported in jfsw.
There is no MIDI data inside the .grp files for the registered version
or the expansions.

There are two choices to get music working in jfsw:

- OGG files, created by ripping the audio from the game CD. This
  works with all versions of the game. To get them, install
  jfsw_registered_data. The other games (Shareware, Twin Dragon,
  Wanton Destruction) will use the same audio tracks.

- MIDI. This only works for the shareware/demo version (jfsw_demo_data),
  and is only necessary if you don't want to install jfsw_registered_data.
  To use MIDI, install fluidsynth-soundfont.