750$ Intel NUC vs $6000 Aurender N200: I don't hear the difference

It is not the issue. Burn in on a server , 150 hours.... come on. That is stretching the realm of believability beyond the usual in this hobby. Swamp land in Florida anyone?

@Cindyment

Thanks, and yes, either could impact sound, and neither is completely easy to 100% eliminate.  All the power supplies and isolation i refer to are custom designed and built by me - as are some of the interfaces and clocks.  So with luck, that's not the issue. I do believe i mentioned that isolation quality varies and I strongly prefer good transformers.

But what i experience is really not the issue. I am hoping to point to issues that many may experience, and why "cut and dry" technical answers give me pause.  I have spent my career helping giant tech companies overcome technical sclerosis that is bred by engineers becoming comfortable with one paradigm or another - things they are invested and expert in.

I suspect that we have a difference in perspective. You seem very comfortable with what you can measure.  I find Audio just full of the "unknown unknowns", things I can hear, but have difficulty measuring.  This is nothing new - once (40 years ago) clocking and jitter was totally swept under the rug.  My objective is to slowly learn what to measure, or at least what design concept correlate with good sound.

“if it measures good, and sounds bad, it is bad. If it sounds good, and measures bad, you’ve measured the wrong thing.” – Daniel Von Ricklinghausen, HH Scott to the Boston Audio Society, 1954

@cindyment

Thanks, and yes, either could impact sound, and neither is completely easy to 100% eliminate.  All the power supplies and isolation i refer to are custom designed and built by me - as are some of the interfaces and clocks.  So with luck, that's not the issue. I do believe i mentioned that isolation quality varies and I strongly prefer good transformers.

But what i experience is really not the issue. I wish i could say "do this, the rest makes no difference. But it does not appear to be that clear.  I am hoping to point to issues that others may experience, and why "cut and dry" technical answers give me pause.  I have spent my career helping giant tech companies overcome technical sclerosis that is bred by engineers becoming comfortable with one paradigm or another - things they are invested and expert in.

I suspect that we have a difference in perspective. You seem very comfortable with what you can measure.  I find Audio just full of the "unknown unknowns", things I can hear, but have difficulty measuring.  This is nothing new - once (40 years ago) clocking and jitter was totally swept under the rug.  We had the same problems in the 80s and 90s when we applied compression to both video and audio, often with studio processing as the consumer. They are not forgiving, nor are blue screens.  And traditional measurements either misled or indicated "it wont work" when in fact, it did.  My objective is to slowly learn what to measure, or at least what design concept correlate with good sound.

“if it measures good, and sounds bad, it is bad. If it sounds good, and measures bad, you’ve measured the wrong thing.” – Daniel Von Ricklinghausen, HH Scott to the Boston Audio Society, 1954

It comes from experience. I have never experienced anything in audio that could be 1) Verified , and 2) Not measured.  Usually #1 eliminates almost everything, and when it does not, #2 takes care of the rest. Every single time where I have heard, or experienced a verifiable sonic difference, there was also a measurable difference. Not just measurable, but above what are accepted limits to hearing sensitivity/discrimination, and significantly different.

I am not talking single point, THD either, but full scans, i.e. THD across frequency and output power, IMD with 2-3 points, and multi-point at multiple powers. Then again, just taking two time correlated streams (digital source only of course) can be highly revealing.

I think we both have respect for isolation, at least for the analog. I do believe a lot of the claims of "noise, RF, pick your poison" getting into the DAC clocking is for the most part suspect. If you know RF, you know that there is more RF coming off that trace 1/2" away then you are going to pick up externally. If the people who made those claims knew depth of D/A design, they would be far more worried about the D/A analog reference :-) ... but also not difficult to regulate for audio frequencies and eliminate noise.

I have convinced myself of things I heard that I later proved were not there. You are so hyper focused that something must be there that you convince yourself there is.

OP could be experiencing sin of omission deal, nuc vs. sin of commission, Aurender. Now is that sin of commission due to Aurrender or some other part of system?

One often doesn't perceive omission as a sin, and it may be preferable in some cases, perhaps in a lot of cases.