I just posted a voice editor for the Yamaha SHS-500 Sonogenic on my web site. The voice editor is a MIDI Designer layout. MIDI Designer is a MIDI user interface development app that runs on Apple iPad. Download the layout from:
It's free. I hope to upload the layout to the MIDI Designer site, too.
Yamaha don't promote it, but the SHS-500 Sonogenic has a built-in General MIDI tone generator in addition to the 28 "panel" voices. The GM tone generator is only accessible over MIDI. (Yep, you can play GM files from a DAW.) The MIDI Designer layout uses the GM tone generator. So, if you're missing drawbar organ or whatever, you can play its GM voice through MIDI Designer via MIDI loopback.
MIDI Designer provides storage for up to twenty voices. (Somewhat confusingly, MIDI Designer calls these slots "presets." Thus, you can store and recall your own voices using MIDI Designer.
If you would like to read more, please see the links below.
All the best -- pj