I successfully had GENPO working with a soft synth (fluidsynth) this weekend. Although the sound quality is marginally lower than using sound-card synthesis, the advantage is that the output can be Jack'd to a real-time FX processor eg. ecamegapedal and you can then use a variety of nice reverb and chorus effects to enhance the 'real organ sound'.
I'll post a screen-shot on the GENPO website soon.
No changes were required to GENPO.