I have resolved all handshake issues for now. I cannot tell you exactly how, but here is what I did.
1. Set everything to run through the Denon receiver.
2. Turned ARC off on the tv and stereo.
3. once I was comfortable with how that was working I went back in the Denon and turned HDMI and ARC back on.
4. set preselects 1. Cable, 2. Blu-ray, 3. Media player., HEOS music.
I turn the system on with directv remote, tv, receiver, and amp come on in sequence. The Denon smart menu displays defaulting to the cable input, I confirm that setting.
if I switch to media player or press the home button on the Firestick remote, the input switches seamlessly. If I want to return to cable I can press the select button in the directv remote, or the preselect on the Denon.
This morning after confirming all of these things worked, I tried launching Netflix from the tv….it worked, with sound.
Thank you all for your responses and help. Again, I don’t know exactly which steps corrected everything, but I will share any settings I have in an effort to help anyone else.