Because my AT is not very smooth i decided to change the atf oil and did a little research.
Here is the result:

The OEM atf supporter for Mercedes-Benz is FUCHS oils.
The recommended FUCHS atf oil for the 722.6 XF transmission is FUCHS TITAN ATF 4134

There is also a Website where you can search FUCHS lubricants for your car:
FUCHS Lubricant Advise

There is also an interesting way to change the atf oil. It was invented by Tim Eckart.
Because the 722.6 transmission has no drain plug for the torque converter, he is spilling the complete converter with a pump system, uses a cleaning fluid to spill out all impurities and fills in new atf oil.
He's also using FUCHS TITAN oils. Clients are very happy with the results.

Website Tim Eckart (german language):
Englisch

Youtube Video (german language, but i think you'll understand how it works)
YouTube - ‪AMG C32 Vorlaufspülung www.Automatikoelwechselsystem.de.wmv‬‏