Set the connected TV/Audio source to output DD+ (for compressed streaming surround audio) and connect the Beam 2 to the HDMi-Arc/eARC port (note eARC is usually required with some TV’s - but not in every instance), then ensure the Movie/Show you’re playing and any App in use supports Dolby Atmos. Note in some cases a higher subscription tier maybe required with the App you use and Atmos audio may only be available on the default English language output setting in some cases, but perhaps check the settings in the App, and/or source device. For uncompressed Atmos audio from Blu-ray Discs etc. then set the codec to Dolby TrueHD - note an HDMi-eARC port connection is (always) required for the uncompressed audio format.

Play the same content from the same source device with the TVs set to the same settings using the same connection method.

Sonos plays what it is sent: there are no options to change the audio format on the Beam.

 I have a 3 year old Bravia.  My TV sound settings are:  eARC mode = Auto  -  Digital  audio out = Auto 1  -  Dolby Digital Plus output = Dolby Digital Plus  -  Pass through mode = Auto.  I do get Atmos when available.

 There is a setting in the Sonos app for Spatial Music, but maybe that’s only for surround setups.  Also don’t know if that has any effect on Atmos from TV.  My room is surround so not sure what effect that would have on your setup.