Go into the dvd player's setup menus, and turn on digital audio output. Set it to "Bitstream", instead of PCM. Then go into your receiver's setup menus, and enable the optical input, and make sure the dvd player is assigned to it. Then set your receiver to "Digital Auto". Your manual should tell you exactly how to do this. You may have to hookup an s-video cable, to see the on-screen display, of the setup menus, for dvd player and receiver. HDMI doesn't usually pass these signals.
The tv is used only for video, in a home theater setup. Turn off the tv speakers (in tv's menus), or have the volume all the way down to "0".
Good luck!
If you still have trouble, post back, with model and brand of receiver, and someone with same receiver will probably be able to give you more detailed advice.