Are you using every output on the cable box? Choose one and go with it. Use only the component out for your video, and use only the digital for your audio.
I don't have the 3805, I have the 1905. Go to the setup menu on your Panasonic and choose component for video. On the denon, go to setup and choose auto. Or maybe vise versa. It's been four years now since I hooked mine up. I'm far from a techy guy, but if I can figure it out anyone can. First start by going simple and follow my first step.