I have a Denon AVR 1700 That has a digital in section on the back where there is an input for an optical cable and two separate coaxial cables. On the back of my digital cable box I have a digital audio out with a coaxial output. I connected one of the digital coax cable inputs to the audio out on the cable box and then went into my receiver's setup and set the coaxial cable #1 to TV/DBS. I thought that this would give me digital sound while watching certain programs, but to my dismay, I get no sound whatsoever. What am I doing wrong?