Are you using HDMI control at all? Are you using ARC (audio return channel)?
HDMI control should never be used, in my experience, as it rarely works as well as expected when an audio video receiver is involved.
Audio return channel (ARC) is only useful if you are hooking sources directly to your TV. So, if your game system, or cable box, were connected directly to the TV on the non-ARC inputs, like input 2 or 3, then ARC would be used. If you are not connecting any of your sources to the TV directly and everything goes SOURCE -> MARANTZ -> TV, then you have no need for ARC to be on. Turn it to 'OFF'.
This may, or may not, help your situation. It could simply be a communications issue between the Marantz and the LG TV.