There are two versions of Atmos for home theaters. TrueHD + Atmos is the version found on Blu-ray discs. Dolby Digital Plus + Atmos is the version used by streaming services such as Netflix, Amazon, etc.
The only Plex client that supports 4K HDR video and passes TrueHD + Atmos is an Nvidia Shield Pro.
Note: I have not tested the new Plex HTPC Windows/Mac application to see how well it handles 4K HDR and audio passthrough.
The Plex app on LG & Samsung TVs will pass Dolby Digital Plus w/ Atmos. It will not pass TrueHD. This is a TV, not Plex, limitation. I am not aware of any TV that will pass TrueHD audio.
Amazon FireTV devices do not support TrueHD audio. It will be transcoded to a supported format. The FireStick 4K supports Dolby Digital Plus w/ Atmos and will pass it to your AVR.
Not all Amazon devices support Dolby Digital Plus. Specifications are online: FireTV Device Specifications.
What you want is:
Nvidia Shield Pro ← HDMI → AVR ← HMDI → TV
Do not use the Shield non-Pro “tube” model. It has problems with high bit rate media, such as 4K HDR movies.
Additional Information:
