Streamers - Auralic, Aurender, Lumin, others...

I had an auralic g2.1 and really liked it. I have now switched to a Grimm mu2, which is a bit better and much more expensive. The beauty about the Auralic was in its fantastic WiFi execution. From what I’ve seen it’s not very common at this level. If that’s not important to you, I’d probably stick with some of the other suggestions.

Playback Designs MPS-X. Best in the world. 

If you can use one of their DAC's too, there is a glass cable interconnect that connects streamer to DAC and eliminates noise and is the best link to use. 

As I mentioned above, Mac Mini is ok as a roon core. But…the purpose built Roon Nucleus One is better. And yes I am talking about using it purely as a core, not connected to DAC. I was surprised to find a difference in sound as I didn’t expect there would be any but the Nucleus provides a more lively and engaging presentation. Not a huge improvement but it’s worth it. Again, if you don’t have a revealing system you may not hear this improvement but at some point I highly recommend you give it a try. 
I thought about why there could be a difference in sound. The only explanation I can come up with is the Nucleus’ mission is much simpler than the Mac’s and it is to run their proprietary OS where main focus and priority is Roon and processing the signal doesn’t involve concurrent irrelevant tasks that potentially deprioritize Roon. There are also less components that can introduce noise. 
I bought the Nucleus because I was annoyed by a frequent need to reboot the Mini or restart Roon app or fighting with impacts to Roon due to macOS updates. I saw a used Nucleus one and snatched it. Improvement in sound quality wasn’t on my mind. 

One other important improvement to sound quality was an upgraded Ethernet cable to either the Mini or the Nucleus. Both reacted to the change but with the nucleus, since it was already an improvement over Mac Min, it widened the gap in performance. I compared these cores in exactly the same configuration - connected to the same router using the same Ethernet cable. 

I’d definitely recommend checking out the PS Audio AirLens. I’ve been running one for a while now and it’s been rock solid — especially with Qobuz Connect, which works perfectly and sounds great.

The AirLens really shines if your DAC has an I²S input. That connection just opens things up — super clean and natural. If your DAC doesn’t do I²S, keep in mind the only other output is digital coax, so that might be a drawback depending on your setup.

Overall it’s a super easy, great-sounding streamer that just gets out of the way and lets you enjoy the music.