I've spent a lot of time with JRiver with Pi's, a NUC, and other Windows PCs, and if everything is working correctly I definitely can't hear a difference between the Pi and the Windows PCs with the same DAC.
The reason I say "if everything is working correctly" is because the Pi can be a little flaky when it comes to power output. So if you have a bus-powered DAC, the Pi can sometimes have a hard time fully powering it. This can be avoided if you use a powered USB hub or otherwise get clever with your power supply design. But the idea that the Pi would provide improved sound quality is unlikely; my experience has been the opposite: the pi is much more likely to have occasional dropouts or other sound interruptions (whether power or CPU related). Additionally, depending on your DAC, linux driver support may be better or worse than windows driver support, which is important to consider.
If you get a Pi setup and have a stable power supply to all components, and the components are well-behaved in a linux environment, a Pi can work very well (darn near perfect), but purely from the perspective of sound quality (disregarding other issues) the Pi only has potential disadvantages over a well behaved desktop PC (whether running windows or Linux). There is no sound quality "upside" other than avoiding a fan (but you can get fanless desktop systems too).
Also, the idea that the Pi would inject less noise into the USB signal requires making a series of assumptions, some of which are probably false. For example, it may be lower power than a NUC, but the electronics around its USB bus are probably not as robust and are definitely not as well isolated as the NUC's (for example the Pi's ethernet port shares the bus with the USB outputs, etc.). So it may (or may not) generate slightly less EMI on the front-end, but much more of it may make it into the bus due to poor isolation. So the pi may, on balance, be effectively even noisier than the NUC. I'm speculating (I haven't measured it), but there are several design features of the Pi (USB bus shared with other components, very poorly isolated analog audio output, extremely low price requiring design compromises, etc.) that argue that they may not have done the best job electrically isolating some of the components. And all of that only matters if you assume that the output of high-quality modern DACs are meaningfully affected by the amount of EMI that leaks onto the bus in a typical PC, which isn't necessarily well-proven at this point.
Of course there are myriad other upsides to the Pi (convenience, portability, price, etc.), but you have to cross your t's and dot your i's to get there.