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?
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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.
Murfie.com 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. 

Murfie.com...will 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