You're welcome, Dieselmartin.
I just called ********, and they want €749 for a chip tuning module, including performance measurement, but without TÜV certification

.
Now, I'm going to look for that '10-cent' guide. Yes, where is it

?
Okay, he then said that it's possible to connect two turbochargers in parallel to get more boost at low RPM. So, not a cascaded setup like on the BMW. I'm just wondering how one would even implement something like that. The control unit will definitely throw an error (regulation difference...), without proper calibration.
Regards,
Mike.