As I said, the problem is to find out how exactly it works between Atari and the Interface on the HW level, so this means on the Atari side of adapter.
Now I have about 75% knowledge I need about this problem. Yesterday I spent some time debuging the HDDRIVER and I think that I probably could get more of that knowledge, but I need to debug more ;-)
Most of the needed information about this is in the Atari ST Profibuch (in German), but not the 25% I'm missing.