* OPL: specify the core to use for playing this song
* FluidSynth: specify a soundfont that should be used for playing the song.
* WildMidi: specify a config file that should be used for playing the song.
* Timidity++: specify an executable that should be used for playing the song. At least under Windows this allows using Timidity++ with different configs if the executable and each single config are placed in different directories.
* GUS: currently not operational, but should later also specify the config. This will need some work, because right now this is initialized only when the sound system is initialized.
* all other: no function.
These options should mainly be for end users who want to fine-tune how to play the music.
