Connect the Arc to the TV’s HDMI eARC port (HDMI 3). Connect the Roku Ultra to any of the TV’s other HDMI ports.

Set the TV to these settings:

HDMI-eARC Mode: Auto

Digital Output Audio Format: Pass-Through

Moderator edit: adding later details for Best Answer:

Well you are truly a superstar!  So no custom settings on the TV or Roku?  I guess with all the new technology everything sort of automatically sets itself for Dolby Atmos, etc?

I appreciate your help!

I posted the TV settings above. I’ll post the Roku Ultra settings later this evening as I need to check my settings. Do you have the latest model Roku Ultra?

...it was a toss-up between the Samsung 990C soundbar and the Arc, but was told the Arc might have better movie dialogue sound, which I need for my challenged hearing.  Looking forward to connecting everything later today.

Yes, I just purchased the new Roku Ultra, so I would like to assume that it is the latest & greatest model.  And yes, I did note the TV settings, thank-you!

Also, want to make sure I download the right Sonos App.  I see the tan background with SONOS across the middle, but the Sonos website indicates the Sonos S2 App would be better to manage the Arc?? 

The Sonos S2 app has a tan background.

Roger that!

Set the Roku Ultra to these settings:

Preferred streaming format: Dolby

Digital output format: Passthrough

Thank-you sir!

Hello,

I have one other inquiry. With my challenged hearing, I am still playing with settings to get the most out of the center channel or better/louder dialogue.  I have selected the voice enhance mode, but could use a little more. Is there any other selections or settings that would further enhance the center channel or voice/dialogue on the Arc?

Thank-you.

Jeff

Not the answer you are looking for…

I tried putting some towels over the right/left speakers to quiet them down making the center seem louder in comparison. The spouse was not amused but it helped.

All we can do is keep asking and hope it makes it onto the Sonos to-do list at some point.