I installed the WebIF, and now it works fine. I could download all the required software and the plugin (had to manually find out, what software was dependant on which other software...).
Now everything works fine, could also record Tatort yesterday
Sometimes during zapping the picture remains black, but sound was there. Maybe it has to do with low signal quality? When I zap to the same chanal a little later, sometimes it works...
Thanks again for the great firmware!