The Amazon Fire TV Stick 4K and the 3rd-gen Fire TV Stick now support streaming music through Amazon Music HD at up to a 24 bit depth and a 192 kHz sample rate. Previously, the only Fire TV model that was capable of streaming the higher quality music was the 2nd-gen Fire TV Cube.
To stream at the improved quality, you need to have the latest version of the Amazon Music app installed, which is v3.3.581, and you need to manually enable HD audio within the app’s settings menu which can be accessed through the user icon in the upper right corner. Of course, you also need to have an Amazon Music HD subscription.
For the Fire TV Stick 4k, the device needs to be running Fire OS version 220.127.116.11 or greater and for the Fire TV Stick 3, the device needs to be running Fire OS version 18.104.22.168 or greater. Check for updates to both the OS and the Amazon Music app under Settings > My Fire TV > About. It’s unknown if other Fire TV models, such as the Fire TV Stick Lite, are also gaining support for the enhanced audio quality.