What makes One Music Server Sound Better than Another?

"It’s about server streaming to endpoint over a network."

That is exactly what I am doing, along with having optical fiber isolation of both the server and the endpoint from the network.

Sorry, should have been more clear - the reason I added that paragraph is that someone always posts about concerns only related to having the DAC connected to the server.  All of this about noise inside the server running down the USB cable.  I wanted to be clear that concern cannot apply to your situation or what I was discussing. 

My plan is to continue using a reliable, well-built, server, somewhere south of $5K,

Part of the point is you don't need to do that, albeit I am not criticizing the choice.  It's more of a matter of convenience if you want auto CD ripping and things like that.  Roon works with any PC with sufficient horsepower to run whatever DSP etc. you want to use.

You won't get any sound bump from any choice unless you hear hiccups or dropouts caused by an overtaxed server, which you can easily determine with the processing speed indicator in Roon.  I have a fairly powerful machine currently running at 60x, meaning I can theoretically support 60 streams before any issue.

Not everyone wants to build their own PCs, I get that.  But it's actually not rocket science and you can build a well overpowered Roon server for $1000 maybe less if you have a PC with some of the parts already that you can salvage (power supply, case, the stuff that gets obsolete less quickly).

My personal view is people buy these pre-built audio server computers because they look cool.  Which they do.  But they're sold with stories of superior audio quality when you get to identical quality with the above plus your chosen streamer.  [Repeat acknowledgment of theoretical possibility of streamers sounding different].

Anyway, I just say this so that when newbies search "what music server should I buy to use Roon" there will be some balance of opinion against those expensive, fancy servers that get obsolete within a few years due to ever increasing CPU, memory, and hard drive speed, when you can upgrade a standard computer for ~$500 instead of spending 4 to 5 figures to replace the whole fancy prebuilt server.   

It is interesting how we are so skeptical of the whys and hows of a better sounding streamer, or for that matter anything in the digital front end.   Sure implementation and components and software make a difference. 

But when it comes to better sounding amps, while we can study the components, capacitance, power supplies, ratings  and schematics, we generally accept that this amp or that sounds better than others. Same with speakers.  Is it the crossover? the cabinet? the driver material? the internal wiring? the placement? the cables?  Or do we all generally know which brands and models sound better?

Our ears tell us if we listen and can hear.  

@jji666

"My personal view is people buy these pre-built audio server computers because they look cool."

That may be for some but I suspect it has as much to do with people being concerned with upgrading every possible component in their system to the highest possible level so as not to miss out on the n’th degree of sound quality.

My server sits in a back room with my network equipment so from my perspective it could look like a cardboard box, as long as it works well.

To the point by @fastfreight about skepticism related to digital front end equipment, I think that is related to our preconditioning that 1’s and 0’s are relatively immune to outside effects so as long as the 1’s and 0’s arrive at the "receiver" intact, the resulting isolation, error-correction, and processing will handle it from that point.  In contrast, most seem to believe that the downstream analog processing (i.e., D/A conversion, amplification, and loudspeaker conversion of an electrical signal to a sound wave) is not immune to outside effects, and therefore believe the music we hear is largely dependent on the quality of the DAC, amplification, cables, and speakers.

“preconditioning that 1’s and 0’s”
@mitch2

Your last post aptly addresses the skepticism around spending more money for a well designed server. There are always going to be those who are completely content with running ROON core on a < $1K off the shelf NUC and then there are those who recognizes what’s needed to get a better SQ from a ROON based setup.