What is the added value of a streamer over a networked dedicated Computer

I have direct experience in running dedicated Mini as both server/streamer and server only. Mine I7, PCIe ssd, Uptone MMK and JS2 LPS, running Roon as server only.

Based on your description greatest liability of present Mini is doing usb rendering within Mini, Mini very weak as renderer. You need to create second ethernet port via bridging of Thunderbolt. This https://audiophilestyle.com/forums/topic/30376-a-novel-way-to-massively-improve-the-sq-of-computer-audio-streaming/ will explain how to do this and also provide great info as to streaming in general! Believe me,  the bridge mod alone will totally transform sound quality!

So, what above means is Mini as currently implemented is far from optimal, the second ethernet port gives you ethernet out to a streamer which will do the critical function of usb rendering. Yes, you could do without the bridge and simply use a switch or router and then go from that to streamer, but this not nearly as good as bridging. This also comes from personal experience via use of audiophile switch.

Bottom line, using Mini for streaming not good, inferior renderer, relatively noisy device regardless of any mods one may undertake.

And then you have liabilities of Mac OS, from what I understand Audirvana Plus does a modicum of OS optimization on it's own, but much more can be done, need third party app wipe, go into Terminal to disable other processes such as System Integrity Protection (SIP), etc.

So, assuming you're willing and able to do all the above, you can have pretty nice server at this point, but a separate streamer still provides very large upgrade for sound quality. But then Audirvana really built for one computer setup, aka server/streamer combo, the server does the rendering. Roon optimized for two computer setup, the Mini or some other server and separate streamer. IMO, running Mini as one computer setup with Audirvana is far from optimal since requires Mini to do rendering.

So, you have the above considerations if keeping Mini. Another path would be to get rid of Mini altogether, if keeping Audirvana get server with optimized usb rendering, assuming you're continuing with usb. I'd seriously consider rendering capabilities of any server you consider for purchase, rendering is second most important component of streaming chain after dac. Point I'm making, many off the shelf servers don't have optimized rendering, which then requires adding a streamer or band aid usb filter 

 I should also add you could continue to use Audirvana with your Mini and streamer. My present setup running Roon utilizes Mini as server only, use Sonore OpticalRendu as streamer, extremely high quality streaming sound quality, beats my pretty nice analog setup. You could use OpticalRendu in your present setup, OpticalRendu has many choices for endpoint implementation which includes ability to use Audirvana. Also possible to implement other streamers with your present setup, just have to do the Mini mods I referred to above for optimal sound quality.

While Audirvana built for one computer setup, you'll still get benefit of superior rendering via separate streamer, problem is you're adding needless complexity. If wed to Audirvana I'd get very nice one computer setup vs keeping present Mini and adding streamer. Roon would be more advantaged with the added streamer. In either case, your Mini needs further mods for optimal sound.

There’s a lot of material on the forums that cover this, but l’m sharing a few posts that I wrote recently to help guide people on what is required in a great digital source, mainly around noise reduction and clocking/timing. Digital signals are very sensitive, and these two areas are the most significant challenges to get right to remove jitter/noise/ fatigue and enable the most natural, dynamic, and full-bodied delivery of digital music.

https://forum.audiogon.com/posts/2440486

https://forum.audiogon.com/posts/2441993

https://forum.audiogon.com/posts/2442047

https://forum.audiogon.com/posts/2445656

https://forum.audiogon.com/posts/2440669

@napoleoninrags16 

I had the same setup some years back. My mini was optimized with SSD and a better power cable, also the software was trimmed to eliminate all unnecessary processes. I enjoyed the hell out of it for a while. Then I got a Melco server/streamer. Everything got cleaner. The resolution was better, the soundstage and instrument separation were also better. The mini was no match. Still, one can live with the mini if it is implemented and setup right and upgrade when ready. If the Melco is a 10, the mini was a 7. 

@napoleoninrags16

You’re on the right track. As long as the digital data is getting to your DAC intact, there’s no reason to get a ’better’ streamer. It’s already doing the job it needs to do.

Jitter isn’t much of an issue. For example, most USB interfaces simply drop data packets if the data stream has too much jitter / error and this will manifest itself as an interruption in playback. If you’re using another digital interface like coax SPDIF or optical, large amounts of jitter will contribute distortion to the signal. If you want to hear what that actually sounds like, here’s a link - Let’s listen to some jitter simulations. Similarly, here’s what an underperforming digital interface sounds like (e.g. not enough jitter / error to cause a dropout).

Noise is another supposed bugaboo. Guess what? If you don’t hear any noise when your system is turned on and set to the volume you listen to, then it’s not a problem.

Digital signals are actually very robust. Think about it this way - if digital signals were fragile, how would the astronauts in the ISS be able to get a 600 Mb connection? How would people be able to stream audio or video from a service that stores the files in servers (which incidentally were probably also copied over a digital network) that are hundreds of miles away?

Yes. A high quality stand alone streamer will provide very large sonic improvements. 
 

I experimented for years with PCs and my Mac laptop… running on battery with most software shut down, with files in different places.

Then I got my first stand alone streamer: Aurlic Aries g2. That in a couple minutes put an end to my resistance to spending a lot of money on what amounts to a computer that looks like audio equipment. The question was dead. No more computers in my signal train. I then worked systematically from the bottom of the Aurender to the very top… and my system is now sonically the same as my great analog side.

Experience completely shut down any logical arguments in my mind. I have reasons I think for the difference… but the proof is in the sound quality. I now listen to streaming 95% of the time.