When using the RCA jacks the digital to analog decoders (DAC's) in the dvd/cd player are used and only two stereo channels are sent to the receiver unless you are using a dvd-audio or SACD player with 5 RCA jacks to your receiver and are playing a multichannel format disc(dvd-audio/SACD etc.) The digital connections: optical toslink or RCA digital cable(copper) send a digitally encoded signal to the receivers DAC's for stereo or multi-channel(surround sound in various formats) output to your speakers (two, three, five, six, seven, nine...)& sub-woofer. For the most part you will be listening only to stereo from an analog source when using the RCA cables even though your reciever may be set to send those signals to all your speakers via one of its digital surround processing modes(DSP's). Sometimes it is preferable to listen to pure two channel stereo direct through the RCA cables but depending on the quality of the DAC's in your receiver there may or may not be better sound doing this. Non-digital sources such as sound from a vcr, off the air broadcast, cable or satellite must be sent as analog signals to your receiver via RCA cables. I hope this starts to answer the question for you.
