I can now control the volume using my Samsung remote on my ARC audio devices. Here's what I did:
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I have an older Samsung TV, and when I used the HDMI/ARC connection to my soundbar, I could no longer control the volume using the tv remote. I "fixed" it by enabling HDMI-CEC using an option buried in the "System" settings on the TV. There was no indication anywhere else on how to do this, or where this setting was.
I did find this information: https://kcscfm.com/samsung-smart-tv-hdmi-arc-not-working/
...which helped understand the issue, and gave me the idea to look everywhere within the setup menu.
It was something like "System", "Expert" (or "Advanced") menu.
Good Luck
