DEVIALET now Roon Ready.

[awkaplan]

1. What do you mean by "the quality of the Roon Core"?  The Roon Core is a software application. It's quality is the same regardless of what it runs on. The computer it's running on can affect things, for example if you're going to use a lot of Roon's DSP functions you need a computer that's fast enough and has enough memory to do the DSP processing or you'll run into problems but you could run Roon on the same computer and have no problems at all provided you didn't perform any DSP functions. There are other things which can affect sound quality, for example I hear differences between output from Roon to my 140 depending on whether I use USB or ethernet, and whether I use RAAT or AIR when I use ethernet but that's got nothing to do with the Roon Core and everything to do with the output choices I make. What are you trying to ask here?

Is there a difference between say an NUC with i7 chip, a PC with same i7 chip running Linux, a PC with same i7 chip running Windows to run as Roon Rock (sorry, got my terminology wrong!   , newbie here)?   Assume they have same ram, disk storage and doing the same thing with a mid sized library, no DSP, no upsampling.   Is the sound quality affected by using a slightly difference platform?  Will adding a linear power supply to the hardware improve sound quality?

I did a recent build of a ROCK NUC.  While "unsupported," I chose the 8th-gen NUC in the i3, low-profile version.  Go for the bigger one if you want to add a second SSD.  Allegedly it performs nearly as well as the 7th-gen i7 NUC, with much less fan activity.  I keep it tucked away in a utility closet, and it has been running flawlessly.  Sometimes needs a reset if I am messing with the DSP, but that is very easy to do from the web-based interface.  Get the RAM (Crucial) that Roon suggests, as it is plenty fast and reliable—the gains of lower-latency RAM in that class are negligible and they may run hotter.  Two 4gb sticks will do you well—I believe that ROCK can only utilize 8gb, so any more may be redundant.  Pick a high-performance NVMe SSD, as that can impact speed as well.  It's overkill, but the higher-capacity drives are allegedly faster, so don't hesitate to throw in a 512gb NVMe SSD, which is where ROCK will be installed.  Roon suggests a 64gb shorter-profile SSD in their guide that is slower.  NVMe seems to be working for me, as browsing with the remote and loading tracks is whip-fast. ROCK OS is super lean and purpose-built, but some extra headroom couldn't hurt unless you're introducing more noise into the build. 

In the BIOS with the NUC, you have the option of shutting off WiFi and other unnecessary features.  You want your NUC wired in via ethernet.

I think building the NUC is probably your best option, and perhaps you'll see better results with a less-demanding processor.  My NUC can upsample, converted from MQA Tidal tracks, and stream DSD64 at 10-12x speed (there's an indicator in the remote application).  I have no need for multiple zones, and haven't tested it.  I regularly see 17x-20x with upsampled MQA files being fed through the Parametric EQ.  

My system is probably not resolving enough to really differentiate between the options you've laid out, but considering what we've all invested in our systems already, building a NUC and getting a decent cable to run from your NUC to your switch is probably your best move.  I ran my core on my laptop (i7 MacBook Air 4gb ram) wirelessly prior, and it was sometimes spotty using AIR.  This was before RAAT support, which has some quirks (starting a song a second or two in sometimes) but is designed (and evolves!) in a way that really stabilizes accurate transmission of quality audio.  I am in the minority here as I connect my to my Devialet via WiFi and use it as an endpoint.  I give it exclusive access to the 5ghz radio in my router, and use a low-power-draw Netgear Nighthawk that allows me to drive it with a fairly inexpensive ultra-low-noise adapter.  I'm in a WiFi-saturated building, but somehow maintain a low noise floor as it relates to signal transmission.  The signal gets there, I monitor the network from time-to-time with Wireshark and ping the NUC and the Devialet from terminal to get a finger on jitter and packet loss, if there is any.

How does it sound?  It sounds pretty good, and the cable you use between your router and the NUC does seem to impact the nature of the sound.  Why?  Don't know.  Because the router and NUC are close to my fiber gateway, I do my best to keep them away from each other and use shielded CAT6a cable for the fiber point -> gateway and gateway -> router.

Roon's messaging seems to indicate that the hardware, aside from stability, is not a huge consideration in regards to sound quality.  The less going on in the background the better, perhaps.  The NUC experience is fairly painless during install and about 1/3 of the price or so of a Nucleus.  It could probably run for years without a reboot under the use you're suggesting. Only hiccup I experienced was needing to assign a static IP to gain stability and reserve that IP through my router, which also allowed me to choose a faster DNS server as well for the NUC.  Devialet WiFi is a tough nut to crack, but when it works, it seems to sound better than a direct USB connection from my laptop using quality cable. 

Build a NUC with ROCK.  It'll take an hour or so to set up, and the convenience of having an always-on, low-power-draw server barely the size of a small paperback will become readily apparent.  Until something comes around in this price range that is stripped of all of the extraneous features of the NUC, possibly further reducing noise, it's tough to go wrong.  And you very likely don't need an i7, and can spring for the less expensive and quieter i3 paired with fast, reliable RAM and an m.2 NVMe SSD.  LPS to the NUC is likely to help more if you're plugging the NUC directly into the Devialet say via USB; if there's a decent break in the chain, especially if you are running things wirelessly, I would highly doubt hearing a difference, even though I'm a big believer in quality mains.