Finally I found this answer in an other forum:
"Go into the BIOS and into the Extreme Tweaker put the AI Overclock Tuner on D.O.C.P and try profile 1 or 2 one of them should read your XMP. The board boots up with safe options by default. If the XMP doesn't work put your Dram frequency and voltage in manually then go into the Dram Timing Configuration and set the ram timings to the manufactures recommendations."
There was a 'profile 1' and this did exactly what it should. I had to allow to increas the voltage (but this RAM was certified for 1.65V anway).
Thank you for your support.