I have been through the tuning process a couple of times. Both times I hit the upper limit of tuning for most of the voices.
One of the VRs when turned (and if memory serves me well, it might have been a global VR) does a strange thing: when I turn it CCW, the pitch goes down but then slowly rises again. When I turn it CW, the pitch rises but then slowly starts to drop. Thus, it's just not possible to tune the Polysix properly. I am not sure where the issue is but it looks to me it could be a capacitor acting up? I might have to check the VR as well.
A couple of checks on the opto-coupler eliminated it as the source of potential issues: it is still functional.
Yash