1 streaming source, like Tidal, Spotify, Qobuz or TuneIn, to mention a few.
2 a streamer to capture the audio stream, with an app to play that particular service
3 a DAC to convert the digital signal into analogue output
4 a volume control plus source selector
5 a power amplifier.
Some streaming units combine 2, 3 and 4 (e.g the Sonos Connect). Others only combine 2 and 3, e.g. the Chromecast Audio or the Apple Airport express, others only serve as 2, e.g. the Chromecast Audio or the Airport Express using their digital output.
In your case, you already have the Dacmagic Plus, which is a DAC with a volume control. The simplest way to use it is to omit the pre amplifier (you do not need one if you are not using analogue sources). Just connect it to your power amps. No need to worry about ’digital sound’. If you are using a decent DAC like your Dacmagic, digital is perfect.
If you do this, the remaining question is how to get the audio stream to your DAC. One option is to use a computer - even a very simple one like a Raspberry Pi is good enough. Use the usb output into your DACmagic and you are done. Roon is nice software to handle the meta information, but you do not need it. Another option is to use the optical digital output of a streamer like the Sonos Connect, the Airport Express or the Chromecast Audio. Your DACmagic will convert the digital signal to analogue, and serve as a volume control. Of these, the Chromecast Audio is by far the cheapest, and the digital output is excellent (the high jitter level will be taken care of by the DACmagic). Personally I am not a fan of dedicated streamers from audiophile brands, as these tend to lock you into their software limitations (and are often obscenely expensive for what they are). Units like the Sonos, the AE or the Chromecast Audio sell in such large numbers that no streaming service can afford to ignore them. Digital standards change fast, and since the output is bitperfect, there is no sonic need to spend big. If you want to spend money on better sound quality, spend it on a better DAC. However, realize that no streaming service offers more than redbook CD 16/44, and converting that to analogue is a piece of cake for any modern DAC.
So, in its simplest form, all you need is a Chromecast Audio and you can get started. Of course, you may want to improve on this by replacing the DACmagic by a Benchmark DAC3, but the sonic benefits will be relatively small. And you do not have to do this now. Get started gently.