Maybe If forgot to mention it in the thread and only mentioned it in emails with Bob, but my tuning cannot work correctly: as soon as I've done C6 correctly for the first voice, I max out VR10 for each voice before reaching the correct pitch, so I cannot really get them to go sharper using the calibration procedure.
I am using a chromatic tuner on Mac OS X for more precision.
I will see if I can use your suggestions with VR15 and the voltage levels.
Cheers.