Soundbar needed a firmware update, so I did that, with no better result.
It took a while to get access to Sony support, you have to set up an account, which I was finally able to do. I sent a query through the site, which got me an email back quickly, with the usual 'unplug and wait for 60 secs' type advice. Of course that didn't work.
For follow up I called the Sony 800 number and got a very helpful young man. He was baffled at the problem, and we kind of talked past each other for a while as I was saying 'pass through!' and he was saying 'but the soundbar has nothing to do with the picture!' Finally we understood each other.
So here's the answer: I needed to connect the Apple TV to HDMI *2* of the TV, and leave HDMI 3 for the soundbar...because as 3 is ARC the signal can go both ways. I was sure that only HDMI 3 of the TV would work with Dolby Vision, but 2 does as well (1 does not).
This works! TV gets the Dolby Vision picture, soundbar gets the audio signal (you have to set this up through the TV's settings), soundbar responds to the remotes for the TV and the Apple TV.
This method of connecting IS NOT DOCUMENTED with the soundbar, in fact all the advice there is, of course, to connect the external source to the soundbar and the soundbar to the TV.
Now I can check other functions, like lip sync and, you know, how the soundbar actually *sounds.*
Hope this will help someone else down the road!
Last edited by Chicago Al; 06-14-2019 at 02:22 PM.