No HDMI out from 4K 85" Sony

Sony support confirms both ends need to be eARC.  An option is optical, but that may not provide better sound than the surprisingly good sound with the Sony speakers, although I think it could provide surround,  I'll give it a try.

As an aside, I was a bit disappointed the beautiful 85" video didn't quite have the impact of the 100" 1080p projection it replaced.  I'll keep my Stewart screen.  Maybe someday the price of 4K projectors will come down.

Any recommendations for a 20' optical cable?

I may have found just what i need.  It appears as though a $50 device from OREI takes in eARC from a TV and outputs HDMI to a non-eARC processor.  That seems too good to be true, but I'll try it.