Most will not be hi res.  If they were originally recorded before digital recording, they cannot be high res as the source was not.  Putting them in a high res package, does not improve the resolution.
I can’t stand amazon and usually stay away , but I did install the app and will give the 90 day trail a go . So far I really like the App,and sound quality has been excellent . Amazon’s app blows away Qobuz and I also enjoy it better than Tidal . I have already canceled Qobuz due to the weak library they have , and Tidal will more than likely be next .great job so far Amazon . 
This is very exciting news for music streaming and I am anxious to use it on my Aurender Music Server.

However, based on my understanding, Amazon needs to build an API for music servers, like the Aurender, Innuos, etc., to use to build their Server Apps (like the Aurender Conductor App) to interface to Amazon. This will take some time. We will see.

I am ready to use Amazon Streaming on my Aurender server. Do you have any information on when Amazon will release their API (if ever)?