I finally received the Robofocus stepper motor back (great x-mas present! :-) and could connect the Robofocus. With the bracket for the TOA 130 scope it was quite easy:
Connected it - worked immediately.
I then had to reconfigure the Robofocus module: change the step size, reverse direction (so that "out" means "out"!) But for some reasons, I could not connect the Robofocus control program anymore. I always got an error that the serial device is already in use. I remembered that I didn't use the control program for quite some time - maybe it was the new USB-Serial converter? I tried one of the cheaper ones (which doesn't keep its serial port) ... and it worked right away. Well, I only needed it to configure the Robofocuser and then could switch back to the newer adapter.
I set the step size to 1 (now the entire range of the focuser is ~5000 steps!), reversed the direction. And was done.
Same night, I configured the auto focus routine of SGPro. I used step size 10 and 15 data points. And it worked beautifully. I also finally understand why it's called a "V-curve" (with the EDGE scope it barely resembled one):