Tidal, Deezer

My whole family uses Tidal a lot.  The sound quality is great and they have a fairly good selection. 
I "off-line" a lot of content.  It is stored on your phone but you need Tidal with a valid subscription to listen.  It's really easy to download music.  When you find a song or album or even a playlist, you will see a little toggle to click to off-line the music.  You can even create a playlist and off-line it.
So, why off-line it?  I download the data via wifi which doesn't use data and is usually faster.  That way when I'm driving or flying I have a library to listen to that doesn't need an internet connection.  And to be honest, Tidal can be quirky and not always get a good connection.  Having music store on my phone helps to avoid interruptions.

Okay Elevick! Well, I guess I can use itunes to build a library. There is one big problem for me. If the files are asc, how do I apply good metadata to the tracks that will give me good cover art? Thank you

I have been a convert to Tidal for the last year or so and all I can say is ... should have done it sooner!

As long as you have a paid subscription (9.99 or 19.99 for hifi) you have access to so much music it is incredible.
Downloading it to play offline is ridiculously easy although obviously it takes up storage space on a phone say, possibly a tablet may be better?

I did try Spotify and I guess I just got so used to Tidal I found its interface and search and play functions to be a little clunky although it seems the majority think it is Tidal that is inferior...lol go figure.

Do not even start with the huge debate raging over Tidal available MQA files, all I know is to my ears the sq is noticeably superior. 

Okay, getting closer to figuring this out. Getting maybe 2 services to provide different functions and greater selection is very appealing. It looks like tidal and deezer elite are great choices for streaming...SQ and all. But I would like to do my offline listening through my computer. Tidal...I don't know about deezer...only goes to your phone or tablet for offline listening, so does spotify go to your computer for offline listening? If I have to give up SQ to do offline through computer I will. 

As I said before, I can do this with itunes, but as I understand it AAC files are no good for metadata? Spotify does mp3, and that would work for metadata provided I can play through computer. Any suggestions? Perhaps a music subscription/streaming not mentioned?

I'm looking at the Spotify app as displayed on a MacBook Air.  Downloaded albums are listed under "Playlists".  When I turn WiFi OFF, these are still available and playable.  I expect something similar will be true for Tidal as well, just haven't tried with it.