Discussion about the Korg PolySix synthesizer

I suspect that you are looking for a way to bypass all of the circuitry 
that is not working and simply connect the controls to the things they 
control.   This would require a lot of re-wiring, and I personally think getting 
the KLM267 working again would be less work than what you are suggesting.
The Poly Six MCU scans the controls all the time, even in manual mode, 
and feeds the results, or the saved settings, out to the hardware using only 
a single DAC.   So it's not really set up to work the way you want, I think.