First, I am an old guy that struggles with this new hi-fi stuff. That said I just upgraded my old Sony 6600 htib (I did say I was old) to a new Onkyo TX NR717 with some new Polk Audio fronts, center and sub. I have Polk surrounds and some older Klipsch in back. I have it set up 7.1. My tv is an older Mitsubishi WD-65732. The tv still works great so I am not going to get a new one until it is necessary. My video source is a set top box/DVR. It is HDMI from the DVR to the AVR. HDMI from the AVR to the tv. Everything seems to be working but I have not run the Audyssey set up program so it sounds a bit anemic thus far. My question is re. ARC. In the AVR literature (what happened to the paper owner's manual??) it states that if my tv does not support ARC I sould run an optical line from my tv back to the AVR. I do not have an optical out on my tv. The only digital out I have available is Digital Audio Out which is an RCA cable, I think. Is this only pertinent to 3D tv and should I make sure it is disabled in the AVR. Any help would be greatly appreciated.