Bluesound is a brand. Bluos app can stream Tidal Masters over NAD and Bluesound and other enabled devices.
I am about to install a whole home system with 4 zones each with a Bluos Node 2i.
They work well and sound about as good as you can get without hunting down other bottlenecks.
Spotify can stream via bluos, bluetooth, airplay, chromecast, Spotify connect or be jacked right into a device with a cable. If you use Spotify Connect or Bluos it pulls it right from their server over a network connection. Depends on your receiver what you choose to use. The other methods above go to your device first, then the receiver.
What are your thoughts on the Bluesound app?
I'm considering at some point moving our legacy Sonos units on and was looking at the Blusound products as an alternative if they die or something fails. I know Axiom has one as well, but a polished feature rich interface is really a key thing. I quite like the Sonos interface but their hardware is outdated and they didn't update much in their 'new' products.
