The streamer and DAC are equally important. Typically it is best to spend equally… similar to turntable and phonostage. I have extensive experience with both. I have this theory that the DAC tends to set the tonal balance and musicality and the streamer will limit the detail and reduce the noise floor. But, they both make a huge difference… and while you can use a Mac book or PC as a streamer do not let anyone tell you it sounds as good. Some technical people put enormous time and money into a MacBook and futzing with their network to get it close to the sound quality of the streamer. A streamer, like Aurrender is a piece of high end audio equipment. You plunk the heavy beast down and it plays high end audio grade sound quality, no futzing like with a PC.
Generally the streamer itself does everything… your iPad acts as a remote control to the streamer. The streamer box has internal software to directly connect with Qobuz or Tidal. There are other ways of doing it… especially in cheap streamers… you don’t want to do that.
Most streamers have internal memory because for a while (a while ago) storing ripped files was a thing. Now with Qobuz and Tidal, these are reliable and of equal quality to any other media.
You can actually purchase albums from Qobuz and download them to your streamer. Also, more or less something of no value any more. I have my ripped library on my streamer just in case my internet goes out. I have used those only a couple times in five years.
The streamed files are not actually kept in your library. What is stored is some data (like the album cover and name of album, artist etc… and a link that you do not see to the location of the album on Qobuz. So press the album and the streamer goes off and finds it and plays it.
A good streamer like Aurender will cashe the music before playing so it doesn’t have hiccups and isolates you from your network. This is why you (I do) can use a network extender plugged in next to your streamer and get top notch fidelity.