Malte, thanks for following up and sharing your settings.
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.