This little device placed between the 4K FireTV and my receiver gives me ATMOS on Prime with my LG 1080p projector.
Wouldn't it make more sense to put the device between the receiver and the projector? That would make it think you had a 4K TV for all devices connected, would it not?
I get Atmos on Disney+ on my AppleTV 4K even with 2K output (only trick is it seems you have to test the "HDR" modes even if they don't work on a 2K projector and then magically Atmos works on everything but Vudu and Prime on the ATV4K that I've tried here (i.e. It works with iTunes, Disney+ and Netflix).