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

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.

I was looking for a stand alone streamer as well as i was very happy with my SPL DIamond DAC. I found the Bricasti Design M5 and couldnt be happier. It has the AES output that i was looking for (as the SPL accepts AES), is a stand alone Streamer (no added stuff), and is made in the USA. 

If you have the chance, i would highly recommend looking into this model.