Dear Windell, thanks a lot, your solution works like a charm. I had the minor problem that first I needed to update the firmware, which thanks to the related wiki-article is easy.
Then the X-axis was out-of-scale. Changing the N_PAGE_WIDTH value did the trick, even though I was a bit astonished that this value has an effect on the motor travel, I thought it only limits the page width.
Cheers
Toni