Hardware sound generators
jOrgan can drive any hardware sound generator that can communicate via Midi.
Almost every soundcard can be used to turn your computer into an organ sampler.
Several products like the Creative Labs Soundblaster series support loading samples in Soundfont format to produce more realistic organ sounds. If your soundcard supports reverberation effects you may be able to achieve stunning performances on your virtual organ.
You might even be able to run multiple soundcards in a single computer. The benefit of multiple soundcards is a much higher degree of wikipedia:polyphony (instrument).
Use the organ samples of your favourite sampler to generate sounds. Many devices support the Soundfont format or you might be able to convert samples into its required format.
If you already have an Organ Expander in your equipment, connect it to your computer and control it with jOrgan.