Control fluidsynth dssi through OSC

First load fluidsynth in ghostess

ghostess fluidsynth-dssi.so

If you click the "About" menu, this will give you the OSC host url, in my case this is osc.udp://localhost:18100
Store the url in a variable for easier use:

export osc_url='osc.udp://localhost:18100'

Next we use dssi_osc_send to send an OSC message to fluidsynth, in this case we will change the soundfont:

dssi_osc_send -C $osc_url/dssi/fluidsynth-dssi/FluidSynth-DSSI/inst00 load /home/michiel/aDocs/soundfonts/all/jRhodes3c-stereo.sf2

To change the gain, use

dssi_osc_send -C $osc_url/dssi/fluidsynth-dssi/FluidSynth-DSSI/inst00 GLOBAL:gain 1.0

To change to bank 1, program 2, use

dssi_osc_send -p $osc_url/dssi/fluidsynth-dssi/FluidSynth-DSSI/inst00 1 2

If you have more than one instance of fluidsynth, you will have to change inst00 to inst01 and so on.