SACD over HDMI

Thanks @big_greg .  The immediate need has passed but good to know 

If you want to use your 105 and send DSD to a DAC, look for a DAC that supports DSD and has i2s in.  With my 203, I send the DSD via the HDMI 2 out to an inexpensive HDMI to i2s converter and connect the i2s to my DAC.  This works beautifully and should work with your 105.  I have not tried this on my 105, so can't verify for certain that it will work, but it should.

No.  eARC is specifically designed to take a signal only from an ARC port of a TV.  A player like your Oppo will not work.  

Actually all is well it turned out that I had to throw a switch on the 20 year old PS Audio surge protector.  Although in the interim I had removed the Bryston and tried plugging it into a different outlet and it didn’t boot on , but when restored to home base with the aforementioned switch turned back it came right up.  However I had Googled around and I read that Bryston dropped the HDMI inputs from their DAC.

  My customer service with Bryston has actually been terrible, with their optical drive and the BDP-3, which I no longer own and took quite a beating on.

  My basic question remains, however; shouldn’t any DAC with an ARC HDMI input work?

The current Bryston BDA-3 accepts HDMI. See here.

Bryston did make a limited run of BDA-3s during the pandemic that lacked HDMI inputs - a consequence of the supply chain and parts shortage.

Bryston has a good service department, so you probably can get your unit repaired.