Hi and welcome to Just Answer. I'm Steve, I'm sorry to hear about your issue. I will try my best to give you a precise and accurate answer.The 1312 doe NOT support ARC over HDMI. Where did you see information to the contrary?
What you will have to do is run a cheap optical cable from the TV to the Denon. You can get a cable from Walmart or Best Buy for a few dollars or buy them for one cent on Amazon :)
Just ask if you need more help on this issue. I will be here.
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Thanks very much.