Hi Adrian, setting the electronic potentiometer with an arduino and some code is not that complicated and I was just about to do it. There are 3 large pads for GND, SCL, SDA, so the connection to the programmer is straightforward.
But then I discovered that the board layout is made for a mechanical potentiometer. Just solder it to the existing pads and move a 0 Ohm resistor to another place on the board. In my junkbox I found a miniature 1K pot form Piher, so the modification was done in some minutes and works fine without loosing the stabilisation and temperature compensation.
My unmodified amplifier had a bias of more than 2 A. Now it is set to 1,2A and this value remains stable even with the board heating up over time.
Adrian, many thanks for your prework and especially for your bias schematic, this was really helpful to check, whether there was a problem with the circuit.
Armin