Amazon has been focussing more and more on audio quality lately, so using the Echo devices as a wireless audio solution for your TV seems like a smart move. Customers who have the current generation Echo and Echo Plus will receive a stereo down mix of a Dolby signal, while the Echo Studio can stream Dolby Digital, Dolby Digital Plus and Dolby Atmos formats. Of course, it only works with content you play through a compatible Fire TV device, and since this works in stereo configuration, it may not meet some people's definition of home theater.
If you want to try this at home, connect your Fire TV device and Echo devices to the same network and Amazon account. Use the Alexa app to select your audio preferences, and then follow the on-screen instructions.
You'll need a Fire TV Stick 4K, Fire TV (third generation), Fire TV Cube (first generation and US only) or Fire TV Cube (second generation). And at least one of the compatible Echo devices: Echo Dot (third generation), Echo (second or third generation), Echo Plus (first or second generation), Echo Dot with clock, Echo Studio.
Update, 7:35PM ET: Updated this post to clarify what formats different Echo speakers support when using the Fire TV / Echo home theater feature.