From the XGIMI site (https://us.xgimi.com/products/horizon-ultra):
1, Press the Settings button on the remote, then select Sound Settings - Digital Audio Out.
2, In Sound Output, choose HDMI eARC output and set the eARC switch to 'Auto.'
3, In Output Format, select 'Passthrough.'
Jgatie thank you for pointing me in the right track. For some reason it doesn't work when visiting the Dolby Atmos official page and playing some samples from them, maybe it's the browser app I chose. (Possibly that's why I kept making tweaks in sound settings to no avail) But after that I tried a UHD disc and was greeted with the much expected Dolby Atmos words right in the sonos app. Thank you again.
Guess I will keep searching for Atmos stuff through internet and see if I can get something now that I have the right settings. My appreciation to you.
