Hmm ok that was what I was guessing too. :/
I edited the /etc/default/xboxdrv like:
# How many Controllers? (support up to 4 Controllers)
CONTROLLER_NUM=1
case $CONTROLLER_NUM in
1) CONTROLLER="-w 0 -l 2 --trigger-as-button --dpad-as-button --ui-clear --ui-buttonmap a=KEY_RIGHTCTRL,b=KEY_F1,x=KEY_F4,y=KEY_F5 --ui-buttonmap back=ESC --ui-buttonmap dl=KEY_NUM4,dr=KEY_NUM6,du=KEY_NUM8,dd=KEY_NUM5"
;;
2) CONTROLLER="-w 0 -l 2 --trigger-as-button --dpad-as-button --next-controller -w 1 -l 3 --trigger-as-button --dpad-as-button"
;;
3) CONTROLLER="-w 0 -l 2 --trigger-as-button --dpad-as-button --next-controller -w 1 -l 3 --trigger-as-button --dpad-as-button --next-controller -w 2 -l 4 --trigger-as-button --dpad-as-button"
;;
4) CONTROLLER="-w 0 -l 2 --trigger-as-button --dpad-as-button --next-controller -w 1 -l 3 --trigger-as-button --dpad-as-button --next-controller -w 2 -l 4 --trigger-as-button --dpad-as-button --next-controller -w 3 -l 5 --trigger-as-button --dpad-as-button"
;;
*) CONTROLLER="incorrect amount of controller specified"
;;
esac
But after a reboot it seems, that it doesn’t load the xboxdrv anymore but the xpad instead. Really tricky. ^^