Generally, no, streaming services to the types of streamer dacs we’re talking about here for home 2ch listening always require an internet connection to play the songs. So you do not "own" the songs if that’s what you mean - but so long as you keep your subscription you can play anything from their vast catalog. I think some services do allow download (e.g., to your phone) and play without an internet connection, but your subscription must still be active (once it expires, those songs won’t play). It’s just that most of the types of streamer dacs described above don’t have way to store. (I hope I’m right about this - if I’m wrong someone will correct.)
I like streaming because it gives me access to vast quantities of music, and it curates them by genre. So, for example, I like blues. I listen to a lot of Albert King, Muddy Waters, Keb Mo, Taj Mahal, Luther Allison, Buddy Guy -- all pretty well known artists. But with Tidal, I go to "Tidal Recommends" for blues and I have access to tons of blues artists I’m not familiar with, and I can listen to any of them any time. It leads to infinitely more time spent listening. That’s the best benefit of streaming, IMO. And it’s CD quality or better if you use Tidal/Qobuz and have a decent player. With Hi Res (different services call it different names) you can do better than CD quality. Will it ever better a high-end vinyl setup? Maybe not today. But down the road, who knows. What lots of folks who have hi-end vinyl setups do is use streaming to identify those albums they want to purchase on vinyl.
Not all streaming services are created equal. Spotify has a free version but the quality is low (resolution). Tidal and Qobuz are the two high-quality leaders, and Amazon has become a new contender, but is not supported yet by many players (Bluesound an exception and maybe couple others).
Establishing an account with a streaming service will involve creating an username and password, that you’ll enter once into your streamer initially, and thereafter it’ll find it automatically each time you power on.
Also, not all players (streamers, dacs, or combo units that have both) obviously are created equally. Not all will play at the highest resolutions supported by the streaming services.
Regarding the dac in your cd player, depending on how good it is you may be better off going with a combination dac/streamer. Besides convenience and fewer cables, everything in digital domain runs off clocks and when you have more devices (like streamer and cd dac) involved there is more opportunity for jitter to degrade the sound quality. That said, if your cd dac is decent, it may outperform the dac in the Bluesound node 2i. Dacs/Streamers improve quickly, as in audio terms/timelines this is a pretty fast moving technology (compared to speakers, for example). The dacs 5 years from now will be markedly better than what we have today. That’s a good thing.
Yes, like everything in audio, prices go from low to nosebleed high. You can find dacs costing $100k if you look hard enough.
