It's confusing for sure. "3D" and "Spatial Audio" are terms used for immersive music through headphones and some Smart Speakers. They can include tracks from Sony's Reality 360 Audio or Dolby Atmos. Sony's is two channel while Dolby Atmos tracks are multichannel and can be sent over HDMI from a device to an Atmos capable receiver/processor. Amazon does not currently support their 3D audio over HDMI from a streaming device. If somebody wants to enjoy Dolby Atmos Music streamed from a device over HDMI to their receiver/processor, there are just a few options. Apple Music, and Tidal are the only services currently supporting Dolby Atmos Music from various devices over HDMI.
Apple Music service Dolby Atmos tracks can be sent over HDMI from the Apple TV 4K Gen 1&2 to a capable receiver. Macs do not support Atmos over HDMI and while the tracks will come over in multichannel form, they will not contain Atmos metadata. Apple Music service Dolby Atmos tracks can only be sent to a receiver/processor from the Apple TV 4K.
Tidal service Dolby Atmos tracks can be sent over HDMI from various devices including the Amazon Fire TV Stick 4K, Amazon Fire TV Gen 3, Amazon Fire TV Cube Gen 1&2, Apple TV 4K Gen 1&2, Nvidia Shield TV and TV Pro and some Phillips and Sony Android TVs. Seems silly for Amazon not to support Dolby Atmos Music from their own service over HDMI from their own devices. If anybody knows if anything has changed, do tell.