The SCI Sixtrak synthesizer featured six voice polyphony, some "layering",100 patch memory locations and limited midi capabilites, unfortunaltely I don't own it anymore... before selling it, I managed to develop a couple of mods for it:

Click here to visit noteit's homepage, where you will find a very extensive collection of resources regarding this synthesizer.

Stereo output, this was accomplished by adding a little six channel audio mixer with pan for each voice and a laboriously (safe) means of extracting the audio signal from the CEM3394 voice chips.
Based on the previous mod, another aproach was to have Individual Outputs, I didn't complete this mod. the schem's and theory are just for reference only, no warranty implied or expressed there, you're on your own ( sorry). On the same context, check out some ideas on how to use this keyboard as a six channel midi to cv controller.