HDMI ARC or Optical out ?

In addition to what already has been mentioned; HDMI will transmit the greater bit rate width for some protocols, but optical is more galvanically isolated.
FYI, some of the better glass cables come from:
Lifatec. Wireworld and DH Labs. Perhaps not as critical, there are lots of HDMI cable options, though videophiles seem to like Wireworld 

 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