Streamer wanted

My experience with interface:
Amazon Music via bluetooth:  easy functionality, not as good as ethernet cable
Spotify just went HiRez by the way. 

Bluesound Node 2i:  Interface doesn't work completely with Amazon but once you get around the quirks, it's OK.  I find the streamer fine but added a DAC and got improved sound
Other streamers:  Interface is downhill from Bluesound.  I am going by what I read FWIW. 

Roon:  Fixes interface issues but costs every month. 

Arguments about need for expensive streamers are like CD vs VINYL, TUBE vs SS.  Regardless it is a great way to find and listen to about any song available. 

As a Streamer ONLY you’ll be hard pressed to find better than a (tweaked) Node2i (upgraded power cord, coax, ethernet cable) without spending big $$$. I was hot for a Lumin U1 Mini until I had the opportunity to play with it. Beautiful little unit however I did not hear enough of a difference to justify $2K and the software seemed buggy. 

+1 on the Raspberry Pi 4 with either Ropiee or Volumio  -- and I do own the Metrum Ambre and the Lumin U1 Mini

My upgrade from streaming from a Dell laptop to my current Roon Nucleus Plus server was one of the best improvements in my system sound quality.  The USB port on the server is "dead quiet" and pairs really well with my DAC and external hard drive.  One of my friends has the Roon Nucleus server and (to me) it has the same fine sound quality and is in the price range you quoted.

One of the great things about the Roon servers is that they come configured with the Roon core and all you'd need to do is add an Android or iOS or Windows app to control it (or all three).  Mine has been "rock solid" with backups and updates.

@rvpiano -- just wondering if you ordered the U1 Mini with an external power supply. My friend who owns the U1 Mini mentioned that adding one had a pretty substantial improvement in performance. I know some dealers can modify the unit to make it work with something like the sbooster.