Other than the room, the biggest influence on SQ is the O/S and @justme, you have come to the right place. Then, linear power supply and various software tweaks including kernel, CPUset, Ramdisk etc.. My opinions using SnakeOil (SO) as the base
- Most of the popular Pi O/S sound worse than SO
- No difference between a Core i3 and 11th Gen i7 using the same software (but I have a special i7 kernel which makes a difference, which I hope AK can use to commercialize SO one day???). Had similar findings with other NUCs, so using a low powered box did not make a difference for me
- NUC is slightly ahead of the Pi5 but had to look for it; in other words, the SQ difference is not night and day,
- Pi5 better than Pi4, based on Mercury which use the compute module CM4
To improve the Pi5, suggest getting a linear power supply or run off battery. I was surprised that running separate boxes for LMS and Squeezelite made a difference (thank you to @hkphantomgtr). And there is a good chance that AK will further improve things...
p/s have parked aside the influence of the room and the use of DSP to improve things. This is a huge topic that should be discussed separately...