yeah, thats it. in the es_input.cfg the controller was missing. only the keyboard was entered.
to get a “clean” .cfg I decided to reinstall retropie – but this time WITHOUT a keyboard. and have a look – now the startscreen can be controlled by the controller 
maybe I will add the keyboard later.
btw: the “es_input.cfg” is stored in /home/pi/.emulationstation
THX 4 help