To enjoy 5.1 dolby digital sound, do BOTH your dvd player and receiver have to have built in Dolby Digital decoders? My Onkyo receiver has built in dd/dts decoders,and the new Onkyo dvd player I'm thinking of buying does not. Can I just hook up my dvd player via digital coaxial cable to my receiver? Will I be able to get Dolby Digital? Or will I have to use that six cable hookup system(2 front,2 rear,1 center, 1 woofer)?

only the receiver needs it. then hook up the digital cable to the receiver. some dvd players need to go into setup to set the digital output some do not. try to just hook up the cable and see if the receiver automatically receives the signal and outputs dolby digital. if not check the manuals to make sure you have everything set right in the setup menus

enjoy!

THANKS, GCRIBBS!

You use this method when your DVD player has the decoder, and your receiver is "Digital Ready".
But for your application, what gcribbs said is correct.