I have a new LG B7 and a Marantz 5012 receiver. I also have an audio problem. The cable box is connected to the receiver by HDMI. The receiver is connected to the TV by the ARC enabled HDMI ports. When I switch to an app on the TV, the sound from the app plays, but the sound from the cable TV does not go off. I assume the receiver is playing the sound from both the box and the TV, but I can't figure how to get rid of the sound from the box! Probably some simple setting I am missing, but I feel like I have tried everything and that this is a basic set-up. Help!