Somewhere in the back of my head is a note remembering a RepRapper with a Gen6 electronics running Teacup firmware and he had no motor movement at all. Unfortunately I can't find the original thread, so I have to open this new one:
Did commenting out X_INVERT_ENABLE, Y_INVERT_ENABLE etc. finally work? If yes, this should go into the official Teacup sources, so others don't run into the same trouble. And
now I have the time to do this