My parents have a great HD2715 C202 Chassis 27E506-00AA. We're trying to get a Sennheiser RS120 hooked to it. I have the red to red and black to white connected on audio out, but no audio is going to Sennheiser. Is there a setting we need to make on the tv to get the output? It is still a beautiful TV and at 84 years old they aren't prone to changing to a new one. Can you help?