Re: extending AV to 2 channel
If it is the 1803 you have then it is not capable of have a dedicated Zone 2 output. You could however fake a zone 2 by connecting your other room speakers to the Surround Back speaker terminal outputs of the Denon. There should be a button on the front panel to turn Surround Backs on and off. Through this use the Surround Backs would function as a Speaker B output. The speakers in your dining room/back deck would have to be connected these outputs. There is no need for a second receiver unless you want the source to be separate from what is playing on the Denon.
If you found som odd need, you could output stereo audio via the CDR/Tape output, VCR 1 Output, or VCR 2 output. These outputs would carry analog stereo audio, based upon its corresponding inputs to another receiver's inputs. However, RCA over long distances does lose a bit of quality. Sending the signal from the Denon to one of your other receivers can only be done analog and probably will not pack a punch.