Yeah the HDMI control bugs me and is one reason i'd use optical rather than ARC tbh, optical really should work very easily. Right when you watch Netflix on the TV go into the sound menu, additional settings, digital audio out and ensure it's set to DD if available. I seem to remember having to do this by pressing Tools and getting into the sound options via that route before but you must do this while watching a movie on Netflix or Amazon. Presumably you are selecting the TV input on your marantz when watching netflix on the TV so it would be correct to have the digital setting to OPT1 against TV (assuming the optical cable is connected to OPT1 of course). Is there a way of switching between the various inputs I.e. analogue / HDMI / optical on the marantz as it might be worth trying that if there is, should work if everything is set like that. If its still not working get back to us, we'll sort it don't worry
Oh BTW if youre not gonna use ARC switch the HDMI control off on the amp, it makes life much easier IMO..