Streaming Music and being able to keep them as your personel files

The Tidal app on iOS (and I imagine Android, though I've never tried it) allows you to download content to your device to be able to play it locally without an internet connection (such as when you're on a plane).  It does need to periodically authenticate with the Tidal servers, though I don't know how often that happens, you could probably keep your offline files offline for at least a week and have them still work, but eventually they're going to stop playing until you allow Tidal to connect to the internet and authenticate you still have a valid subscription.  

I wonder if it’s possible to record the Tidal digital signal off the digital output of my Esoteric DAC as Tidal streams through the DAC in real time. I have a Tascam digital recorder that should be able to pick that up from the DAC's RCA digital output and record it.  Alternatively, it's a straight-forward process to pass a DAC's analog outputs into the Tascam's ADC for recording.  However it would be nicer to avoid multiple digital-to-analog conversions by keeping the process in the digital domain.

Spotify too lets you download music to a local hard drive for listening while off-line.  You don't own the music outright;  you need an active subscription and must periodically re-connect to Spotify (1x/mo?) to maintain access to the downloaded files.