I do use that setup sometimes. But since wiim releases the nice Wiim App for Fire TV visualization is no longer a reason to go for Amazon Music at Fire TV.
I rather use the app Amazon Music with my phone and enable Alexa Cast through my Ultra. You'd enjoy the Amazon Music official app while it is Wimm Ultra streaming the audio. The other option is to use the wiim home app's amazon music interface (i agree not so nice, many threads here about what lacks and fails).
Anyway Let me advise settings for best audio in your Fire tv and TV settings
- Fire TV audio settings
- Display & Sounds - Audio- Surround Audio
--- If using ultra hdmi for movies use 'Best Available' setting
-- If using hdm just for stereo you may also chosen PCM ( best available is also fine)
Either way and regardless what the song resolution is and regardless of what the amazon music interface says on screen the Ultra will receive most likely 16 bits/48khz audio resolution (AC3 OR PCM). Maybe if toir TV is verinmodern and eARC it may go with higher sample rate. You can check that in the now playing screen off Wiim Home App.
TV audio settings (the most important if you don't want poor dac/dsp to mess around with your signal.
It depends on your model wherw to finde the setting but typically you should look for the audio settings , optical / hdmi output and select 'Passthrough' as prefered option . If that does not exist then PCM
But my advise is to use native amazon music app on phone and give a try to wiim app on Fire tv.
You will no longer needed amazon music app on Fire tv just for the enjoy of lyrics and big album art.
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