Mini PC as a streamer

Good point about the RPi -- if you use the USB output, make sure you get a model 4 instead of 3.  The model 4 handles USB output fine.

Not worth trying. For what purpose?

If your goal is to play music files from local storage, I recommend you skip Intel NUC and go straight to Intel SoC mini-ITX motherboards, such as ASRock J5040-ITX.  The motherboard comes with Intel Pentium Silver SoC complete with fanless heatsink.  Using low-cost and low-powered mini-ITX motherboards allows you to upgrade to better power supply later on without breaking the bank.  Can also add audio-grade USB card.  Can have separate power rails for internal SSDs.  All these affect the SQ.

Intel NUC has limited upgrade paths.  Converting Intel NUC to fanless case is very expensive.