Digital streaming/library

I have purchased a rather substantial 2 channel audio system, and two of the components are a streamer and an audio nas...a melco. I want to build a digital music library. I would love to have the hd level tracks, but the downloads are so expensive. I already have thousands of lps, and thousands of cds. I have iTunes, and it (and rhapsody) allow you to download tracks into your computer...but they are not cd quality. I have a streamer, and I could get the tidal or deezer hi res subscriptions, but do they allow you to download tracks into your computer/nas drive for a digital library?
easola01, I would check first if you can hear any difference between formats.  In addition, many high res files are just 16/44.1 up-sampled.  They end-up with more bits and higher sample rate but don't carry more information.  My DAC up-samples data anyway.  I also have thousands of CDs that I keep on external hard drive in ALAC.  I Wi-Fi them to Airport Express that feeds Benchmark DAC3, using ITunes.  With this scheme I'm limited to 16/44.1 but don't have to worry about anything related to computer (speed, playback program, amount of memory, electrical noise etc) since my DAC always gets bit perfect 16/44.1 data.
Get Roon and Tidal. Enjoy your private collection and an extensive streaming library at the same time...

Make sure Apple Core Audio (audio midi setup) and Apple iTunes are both set to 16/44.1. Core audio is a terrible SRC converter but the one in iTunes is good. Avoid at all cost any Core Audio conversion.
Shadorne, I thought I checked it but it was long time ago.  I will check again.  Thank you.

I don't understand kijanki. First you say to setup audio core, and then you say avoid audio core? I am brand new at this, so my understanding is very limited. you can download music files from tidal for a personal music library?
Also, yes I can download itunes for a library, but it is in, I believe, 256kbps...not even mp3! If I want 16/44.1 music library, how can I get it? Hopefully through tidal or deezer
I don't know about deezer, but you cannot download tunes from Tidal.  They stay on their servers, you pay a monthly fee, and they stream them to you on demand.  With the correct version of Tidal, you will get 16/44.1 aka CD quality data stream and there may be some higher rez formats supported also, but as others have pointed out, often the source material is lower rez and the hi-rez stream is just up-sampled.  As far as I know, the way to get CD resolution material onto your NAS is to either buy CDs and rip them, or buy CD quality downloads. 
Well, I guess I will have to stick with itunes then. With itunes, you can download tracks/albums right into your storage device. Rhapsody too. I was hoping to get better resolution than the 256kbps from itunes, but okay!
easola01, It is best to avoid conversion by Audio Core.  Because I play 16/44.1 I set Audio Media to 16/44.1.  I tunes gets my CD without any conversion as 16/44.1 and sends it to Airport Express as a data.  Airport Express send it to my DAC as 16/44.1

Shadorne, Audio Media was set as 16/44.1    In fact AirPlay was not even shown as output device.  When I added it, it showed as 16/44.1
Okay thank you kijanki, but I am wanting to build a library from what will be a boatload of music I do not possess in cd I don't possess and music I haven't heard yet but will while I am browsing my streaming. I am just surprised that, given the fact that one can build a library with itunes and rhapsody, both which are lossy, that there is no comparable way to do the same and build a library in lossless files?
easola01, I'm not familiar with streaming.  My whole library consist only of CDs on HD  in ALAC format.
Thank you for your input kijanki. I must confess, your informed advice is above my head, but I want to do things right. Since it seems I am unable to build a lossless library from tidal or deezer, maybe I will do what cds I have your way. 

So what do I do...are you saying I need to get this audio media, and that alone will convert cds to library from itunes to my storage as 16/44.1? Sorry, I need baby steps here
I rip data out of my CDs using (free) XLD for MAC.  I store ripped data in ALAC format, that is lossless compressed file.
Perhaps the best program you can use with Windows is free EAC (Exact Audio Copy).  This program will try to go over same unreadable sector more times than ITunes, that eventually will start interpolating or even dropping out samples - big advantage with scratched CDs, not so much with new.  Selecting format to use is another story.  ALAC, that I use, is more of an Apple thing, while FLAC is not supported by Itunes.  Best choice for you might be AIFF because it can hold metadata.  It takes more space than FLAC, but storage is cheap, these days.  Be sure to create backups.  
Okay. I have read that flac is the way to go for metadata and sound quality combined. Is AIFF as good and thorough for metadata as flac do you think? If not, I may have to go another way
AIFF is as good as FLAC but files take roughly twice more space.  ITunes doesn't play FLAC. has a marketplace where you can buy CDs and download the files from them in FLAC or ALAC. You can't get files with higher resolution than 44.1/16, but it's much cheaper than HDTracks.
Wow, twice the space. That would be like a wav file. Maybe aiff is lossless. Thank you for advice kijanki. look into. Hope they have a good selection! Thanks
Okay, I am now a bit confused. I read that tidal allows you to download tracks for offline listening. Isn't that a way to build a music library? If you can download for offline listening...I don't understand why that wouldn't be a music library. Does anyone have experience with tidal on this? Thanks