Thank you! I have my IR profile set to the SB series...but now I will try VSB. My other settings have been jacked around with my troubleshooting efforts, but I will reset them to factory and will see if that helps.
Unfortunately, I won't be able to try again until the following weekend, but I will try then and will report back.
I really appreciate all of the comments and suggestions!
I'm also glad you found a few pearls to make it worth your time!
Update, I tried changing the IR Profile to the "VSB" series instead of the "SB" series (mine is SB, too), but no joy. I also reset the IR timing and repetition to default, to try and replicate your settings. Unfortunately, no change. I still have to be 4 feet from the soundbar to get the Fire TV Stick 4K Alexa remote to control the soundbar volume. I can use the native Vizio soundbar remote (which I hate) or the Charter cable remote (which I programmed to operate the soundbar), but I would really like to get the Fire Stick 4K remote to work properly from where I sit, 8 feet away.
Thanks for all the help, but I am at a dead end at this point!
If I select 10 bit YCbCr my Optoma UHD51 show 10 bit 4:4:4 playing Prime video
It seems that this cannot be changed. The result is that sometime the video signal is lost and I see also some horizontal white lines on the screen. Most of video content is 4:2:0, I don't understand this behavior, the output should default to original format.
I don't have these problems with Jriver using MadVR, so this is not a limitation of my equipment. But MadVR is sending the right output (not 4:4:4 if the source is different)
I think that Amazon should give an option for 4:4:4, 4:2:2 and 4:2:0