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.
I've spent all day trying to connect my cable box to my receiver, which is connected to my TV. I get audio, but NO VIDEO.
These are my components:
1) Time Warner Cable HDTV Box: Pioneer Voyager BD-3510HD aka "Cable"
2) Denon AVR 3805 aka "Denon"
3) Panasonic 50" Plasma aka "TV"
These are my connections:
Cable to Denon
1) Component video (red/blue/green) from Cable "Video Out" to Denon "Component Video 2 In"
2) RCA audio/video from Cable "Video Out" to Denon "Audio In" (red & white) and Video In" (yellow)
3) Digital audio from Cable "Digital Audio Out" to Denon "Digital In Coax. 1"
Wall to Cable
1) Coaxial/RF from wall to Cable input jack
2) A/C adapter
Denon to TV
1) Component video (red/blue/green) from Denon "Component Video Out" to TV
On the Denon Input Setup (3.3), I've assigned TV to VIDEO2. Also the "Video On" is on (vs. off).