Hi @Kristian_5.

Thanks for reaching out and congratulations on having a new Sonos product, let me help and try to figure this out.

ARC and eARC are protocols responsible for sending audio over an HDMI cable to home theater sound systems.

Sonos speaker like Arc can only play what is handed to it.

To identify what audio signal or audio codec the TV is providing on to Sonos, using the Sonos app please navigate to:

Settings > System > About my System > Sonos System Info > Audio In

The hardware you’re playing it on has to be able to decode Dolby Atmos or pass it along to a Dolby Atmos-capable sound system without altering it. This is known as “pass-through.”

Some TVs do not support Dolby Atmos audio even if the source device does, so the TV will re-encode the audio to Dolby Digital 5.1.

To know if the TV has this function, please consult the TV’s user manual or manufacturer for specific instructions and settings.

For more information, please see this article that outlines the main factors to Listen to Dolby Atmos on Sonos Arc.

Let us know how it goes and if you have any questions feel free to reach out, we’re always here to help.

Your question is a bit mixed up. The XBox doesn’t send an ARC signal, it sends an HDMI signal. It’s the responsibility of the TV to create and pass the ARC signal back to the Sonos. 

The XBox manual should be able to tell you if it can send a Dolby Digital signal, but then you’ll need to see if your TV can send it out via ARC.
 

Mine, for instance, can’t. It’s an issue with the HDMI input, not the ARC output, since my TV can send Dolby Digital plus only from built in apps, and not from HDMI sources. A bit messed up, so I’ve chosen to order the HDFury Arcana, as discussed here.