Amazon HD and Ultra HD are supported in the WiiM Home App and the native Amazon Music App via the Alexa Cast. To use the Alexa Cast, you need first to log in to your Alexa account on the WiiM Home App by selecting the Browse tab > Amazon Alexa. Both options support the bit-perfect audio output and gapless playback up to 24-bit, 192 kHz.  

The Amazon HD is lossless audio in 16-bit, 44.1 kHz and Ultra HD is in 24-bit, from 44.1 kHz up to 192 kHz. Please find more details here.

1. The Amazon Music on WiiM Home App.

2. Alexa cast from native Amazon Music App.