do i still need a pre-amp

Yes .. the current comcast box i have has a digital out.

seems like the good news is there no need to purchase a new pre-amp since my old one should work

thanks for the help
now just need to come up with the money for a new panasonic plasma

Does your cable box have a digital audio out?

The signal being output by the TV will be Dolby Digital stereo or surround depending on the broadcast

It depends on TV. Panasonics output Dolby with digital and PCM with NTSC automatically. Since NTSC is gone you would be stuck with Dolby. There is no menu to switch it (unless newest TVs have it). Samsungs have it selectable in the menu. Better check it before you buy. I have Samsung LED connected to two channel DAC.

It sounds right to me. I guess that answers your question, you still need a preamp.

thanks .. My cable is wired and has digital out as does my DVD player and my rotel has two digital inputs so if I understand correctly ...
HDMI from cable to TV
HDMI from DVD to TV
Digital from Cable to Rotel
Digital from DVD to Rotel

So to watch TV, I use the source control on the TV and for sound the processor?

thanks

What LoomisJohnson suggested will work provided that you have cable and that your cable box has analog outputs. If you are receiving your signal over the air and your TV is doing the decoding then the suggestion will not work.

Very few if any TVs today have analog audio outputs, only optical. The signal being output by the TV will be Dolby Digital stereo or surround depending on the broadcast. If this is your case, then you are going to need a processor with an optical input to convert the Dolby Digital Signal to analog stereo.

keep your rotel preamp; connect your cable box and bluray by hdmi directly to your tv (for video) and also connect red/white rca from cable box and bluray to your preamp for audio.