Isolating or being isolated, that seems the question if indeed each is contributing significantly to network isolation.
It seems we have acces to a vast choice of good switches (with low-noise, stable oscillator for the main clock), good power supplies , good cables and good network cards for optimizing signal routes, minimizing reflections, interference, and crosstalk. Add to that some strategies to isolate the hi-fi network from the home network that can improve sound quality. Finally we are awaiting modem/routers that need to be improved or developed according to these specs.
Do keep in mind that playing (only) local files vs. streaming is less demanding on the network (isolation). But that could all change in the near future when they will sound the same ; -)
image : Stillpoint isolation