I've tried every statistical combination of inputs and outputs, settings, etc. But I still think there's the right combination somewhere between the TV and receiver. I've tried every combination of HDMI in/outputs. Replaced the optical audio chord with one straight out of the wrapper. On the receiver I've tried all the HDMI inputs (four of them), Audio 1 and 2, all six AV inputs. I've tried the same combinations of HDMI and optical audio outputs from the TV. The only output I haven't tried is one that's a small pin jack output...the kind of pin jack you'd see on a cell phone. It's not like any output jack I've ever seen. And we're talking about a fairly recent smart TV (about two years old). I think it's a digital audio output. There is a window that appears that shows all the outputs and the various speaker and HDMI combinations. I've tried them all...numerous times.
Although I'm not much of a computer whiz I have hooked up countless sound systems and have never had the challenge this has presented. The receiver is a Yamaha RX V765. It's working fine in all other respects. Here is a link to the owner's manual for the TV:
file:///C:/Users/tessi/Downloads/MFL69272402_01+MFL69289402_00.pdf
This is the link to the owner's manual for the receiver:
https://usa.yamaha.com/files/download/other_assets/0/334940/RX-V765.pdf