There are generally three options to hear audio from a cable box on a home theatre system. They are HDMI, optical audio and RCA audio.
HDMI cables can carry audio and video from a cable box to a home theatre system, which then must be rerouted to a television. If someone is interested in only audio, HDMI cables are still a great option. To connect the cable box to the home theatre using HDMI, simply plug the HDMI cable into the HDMI OUT port on the cable box and into the HDMI IN port on the home theatre system. If the cable box or the home theatre system do not have HDMI ports, choose a different option.
Option two is to plug an optical audio cable into both devices. Simply take an optical audio cable and plug one end into the DIGITAL AUDIO OUT (OPTICAL) port on the cable box and plug the other end into the DIGITAL AUDIO IN (OPTICAL) port on the home theatre receiver.
Finally, red and white audio cables are the last and the oldest option. Simply take the white and red ends of the audio cable and plug them into the corresponding red and white AUDIO OUT and AUDIO IN ports, designated L and R, on the cable box and home theatre receiver.