Amazon HD Lower Price

Unfortunately, Amazon HD sounds terrible.

Need Roon to support Apple Music Hi-Res.

don't mix Amazon in with the other 2 you wrote about 

Well, I have Amazon HD and I'm able to stream 24bit/192kHz through Fire Cube to NAD M17V2. I can also stream Amazon HD through the BluOS, but I prefer the Fire Cube / Amazon Platform using the FireTv remote instead of an app, using the phone or computer. Also Amazon Music include lyrics on most songs. Both streamers will do 24bit/192kHz. Bluesound has a little more laid back sound, maybe a little bit cleaner, less noise, but not a big difference. I had Tidal Music service along with Amazon Music and I still preferred Amazon. I'm very happy with Amazon Ultra HD.

Dyson 2004

"When Apple roll out their HD service in June, how do I stream their music through my external DAC? Their Apple TV box doesn’t have any digital outs except HDMI. I can’t think of a way to do it."

You need to hard wire a streamer to your DAC. I use a lap top to run the Music app then USB to the DAC. Wireless Bluetooth does NOT support HD music streaming.