Oh, I missed that post. You shouldn't have reminded me though as it severely impacts your case

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Let's start with the video in that link:
http://archimago.blogspot.ie/2013/03/measurements-hunt-for-load-induced.html. He runs an audio encoding with dbpoweramp with all CPU cores whaling and nothing, absolutely nothing happens in the output of the DAC over the usually lousy internal Toslink of the motherboard. Remember, playing music takes zero CPU cycles in a modern PC. The load that he generated there is millions of times higher and it still showed no impact whatsoever. That is in a spectrum analysis that is showing constant jitter/noise at -110 db. In other words, whatever may be there is buried well below these levels -- precisely what I was saying my test showed.
Now as to our point regarding that bit of noise, let's examine that. This is with the system idle:
This is with the system going nuts, with all CPU cores 100% busy and GPU maxed out to death:
Folks looking at this wouldn't know of any problems without reading the text and then squinting. What he is noting is that tiny, tiny rise in noise level between 8 and 9 (KHz) markers. That increase is from -140 to -130. And here is the key thing:
this test used the motherboard DAC. So sure, if you are using the onboard DAC, things can leak onto it. Certainly to this level. This is super tiny impact.
BTW, look the evidence of what i said about making this worse sometimes. Look at that spike at 11 that vanished with load! Great evidence of how unpredictable the PC can be.
In my testing, which I assume is representative of the interest of people in this thread, I was using high-performance async USB to outboard DACs. I bet if he had used the same fixture there would not be that noise. If there were, then I would get a better USB adapter!
I actually have no problem accepting that an internal DAC in a PC would be noisy and at far higher levels than these under massive system load. Ditto for Toslink. But that is not the AB scenario that we are discussing. Our case is where CPU load remains minuscule in JPlay or no JPlay. And GPU is probably idle other than displaying UI and changing it from time to time. And one would hope the audience who cares about such things has a high performance interface to the PC which isolates it from that box's noise.