Yours was an interesting post and raises interesting concepts, but there's no way to answer your question. I'll also say countless people have been debating this for years, largely without evidence. Google "audiophile linux vs windows".
There are any number of real factors that could account for real audible differences. They are legion, so I won't bother listing any.
Your overall description, however, is so vague, scientifically speaking, as to be meaningless. It's another anecdote. If you want to make claims that stand up to any kind of scrutiny or analysis, you have to scrupulously document the configuration and control the environment. Since you have mentioned nothing touching on those issues, there are no conclusions to be drawn from your anecdote.
Looking at the Playback options in JRiver, there are 32 different permutations available. Of these 22 do not work (no sound) and the others appear neither to add nor detract from the reproduction quality
This concerns me though. I'm not sure what "playback options" you refer to. But the over simplification of this statement is troublesome. Because if someone was referring to the MC audio options than control interaction with the audio device and how audio data is formatted, and that someone believed those settings do not affect playback quality, then that someone bluntly doesn't know what they're talking about, at all, and everything they say on the subject has little credibility, and they need expert assistance. Or maybe you were talking about trivialities, like repeat, which indeed have no effect on playback quality. You didn't specify.
But as I said, there are any number of real factors that could cause real, non-imaginary, audible differences. You might have the systems configured differently without knowing it; your DAC might be highly susceptible to jitter differences (some are, some aren't); a badly engineered component might be spewing or receiving RF leakage that is causing data corruption; a badly designed driver might be resampling audio when it shouldn't.... The list is endless.
But if there are real differences, that is easy to assess. If there is an audible difference, it can be measured.
With the aid of your "electronics scientist" get an audio analyzer, and measure the audio data coming out of both Operating Systems. They will either have differences, or they will be identical. If they are different, then those differences can be analyzed and hopefully explained. If they are identical, then the audible differences you hear are either caused by a downstream component, or they are unreal.
It is often thought that any perceived differences in sound that are unreal, in that they do not actually exist as real-world forces, are imaginary (expectation bias, placebo effect, etc). But this is not true. Often ignored is the complicated physical interface that exists between the real (the sound waves hitting your eardrum) and the perceived (what you hear). And that is the brain and nervous system. The human brain is a lump of jello. Nothing is repeatable: the neurons fire differently every time something happens, guaranteed, even if the stimulus is identical. The perceived frequency response of your ears changes with your blood pressure, your mood, your physical position, the temperature, the time of day, whether you have the sniffles, your medication, everything. Including what you're listening to. And that's just for starters.
The concept is easily demonstrated in a way not subject to debate: someone who squirts water into their ear canal will experience a definite alteration in what they hear, not an imaginary one. And yet, the sound coming out of their speakers will be exactly the same.
Audiophiles often claim "everything makes a difference". They think that if they hear it, it is real, and it must be due to some external component, like a green marker on a CD, or a rock, because they believe their own perception to be invariant. But it is not: their own perception is highly variable (you at least partially recognize this, in your reference to a glass of wine). That doesn't mean all the differences they hear are unreal, but it means some of them are: they are differences in perception only, not in external reality.
I don't know what you heard, or think you heard. Try measuring it. If it is as consistent as you say, you will be able to measure a difference somewhere. Then analyze it, and contribute to the community by explaining it.
Contrary to how it might sound, I actually have zero interest in debating with people things that they think make their system sound better, whether that's cables, or DACs, or amps, or green felt markers; people should please themselves. But if you can actually demonstrate and quantify output differences between operating systems over the same hardware when both claim bit perfect reproduction, that would be very interesting indeed.