Here's my own experience of this; I use Amazon Ultra HD (their term for hi-res, better than 16/44.1) for music streaming for a number of reasons (family accounts being a big one) and found it incredibly frustrating to get hi-res quality music out. It's even more frustrating to get clear information!
Started out with a wired connection from my phone to my DAC (Chord Mojo, about to be replaced with an ASR recommendation) - sounded nice but it tethered my phone. Fairly sure the audio resolution was limited by android. Need my laptop for work, so that wasn't a viable option.
Ended up with a Bluesound Node (pre-loved on eBay to keep the cost down). The interface is clunky but the sound is great. This works for me and I'm really happy.
Along the way I found out that Heos or Play-Fi would probably have done the trick too, but I couldn't find anything better than the Bluesound for the price.
Amazon's Echo Link was a tempting option, with the restriction that it's limited to CD-quality (and it resamples). I probably wouldn't have heard the difference and it does look neat.
Fiddling with FireSticks and Cubes was an option, but seems like you really need an AVR to make that work reliably (and I don't). Too many stories of HDMI audio extractors also limiting the resolution and many, many stories of pain and frustration.
Amazon are not (not at all) helpful ... good luck with this!