OK, now I got it :-)
The tuner is now visible in E2 but it still doesn't work, when I record something with the first (internal tuner) I cant switch to another mux, its grayed out. When I disable the first tuner, so only the USB tuner stays active, I get no signal.
The blue LED on the stick behaves the same, it goes on during the boot but after a couple of seconds it goes off and stays off.