It's a new Roku TV. It has an ARC jack, and the Marantz has one, too. The TV tells me the ARC connection is live. And in the Marantz settings, I activated the ARC connection, but I still have no sound.
I recently bought a Roku Ultra. I hooked it up to our 8 month old LG OLED Web OS TV. Supposedly they both support all the latest bells and whistles. Even though my home LAN is all wired GigE with managed switches, I decided to hook up the "main" TV via an HDMI interface. The "best" one according to my LG.
The Roku did a handshake with the LG. Installed ARC and Dolby vision... whatever... no audio, the screen would flash every minute and the video quality sucked.
(1) The HDMI cable, which was two years old and works great when I connect my laptop PC to the TV works flawlessly... guess what? It doesn't work with the latest standards. So, I dug out a new "8K" cable, and the flashing worked.
(2) Dolby Vision sucks. Looks terrible. I always set my TVs to "cinema" mode but Dolby Vision overrides that. It sucks. It makes everything look cartoonish and disables user modes. Adios, junk...
(3) I ended up "down converting" the interface to a "plain jane" 4K TV. No Dolby Vision, no ARC, nothing else. Now it works fine.
The "standards" in consumer video are NUTS. Good luck. Try to avoid all the doodahs... just run it as simple as possible. Disable one thing at a time.