HDMI ARC or Optical out ?

 If you go Optical, then go glass.

Yes the best glass with ATT&T bnc type connections (aka Wadia and Esoteric used with their top units) with a dab of  very $$$$$  "Indexing Fluid" on each end so there's no air gap.

Cheers George

I could be mistaken, but I thought there could be some compatibility concerns when using AT&T with Toslink.

First , thank you to all who have responded !
I kind of thought that it would boil down to " try-and-see ."
It was worth a shot . I do have a nice DH Labs cable but not a HDMI
cable .
Marching on .

Be Safe 

@saki70   The DH Labs HDMI 2.0B Silver is a solid value and performer. 

David ;
  Thank you .