Amazon Music High Definition and Ultra High Definition Equipment Requirements

The BluOS platform has Amazon Music as a native option within the app…not a casting one like Spotify or Tidal Connect.  The Node N130 is the device to fulfill your objective.  But if all you want is Amazon Music the Echo noted above is more economical, although its onboard DAC may not be as well implemented.

I second the suggestion for the WIIM Mini (or the pro version for that matter.) I’ve had mine since June of last year, and am quite happy with it’s functionality. I bought it specifically because it allows me to stream high res Amazon Music bit-perfect to my DAC while using the native Amazon app on my phone.

The WIIM app is not terrible, but like most other non-native streaming apps, has it’s limitations. That said, it does have some cool features like multi-room audio, content presets, DLNA, and global searching across services. It also integrates with basically all of the music streaming services, which allowed me to compare and contrast the different offerings to see what I liked best for my own needs.

At their price-points, it really seems like a no-brainer type solution that’s worth every penny!

Oh, and not to ignore your question about the Modi+ - That's a fine budget DAC that would work well with the WIIM, but don't think the iPhone would be a great solution at the end of the day.

You will need one of these to grab the digital data from the phone to send to the DAC. 
If the USB in the DAC has power, it can power and charge the iPhone. 
https://www.amazon.com/Apple-Lightning-USB3-Camera-Adapter/dp/B01F7KJDIM/ref=asc_df_B01F7KJDIM?tag=bngsmtphsnus-20&linkCode=df0&hvadid=80401905752532&hvnetw=s&hvqmt=e&hvbmt=be&hvdev=m&hvlocint=&hvlocphy=&hvtargid=pla-4584001431258757&psc=1

@mwinkc 

yes, one advantage of Amazon is being able to directly handle many streaming services.  My CA handles only Qobuz and Tidal, everything else requires AirPlay or Chromecast 

Appreciate everyone's input. I believe I am converging on a solution.

Stay tuned for further developments...........