It's just that the files are storred directly on the music server. Network is used only for controlling playback via a remote app. Router is 15m away on a different floor. It's fascinating that in this scenario there is a night & day difference in sound quality depending on which network adapter is used.
If you recall, most designers expected that when USB interfaces became async that the USB cable and computer would not matter anymore. We know how that turned-out. I have theories as to why this occurs with USB.
For Ethernet, there is leakage across the transformers. This is why the isolators and earth-grounded DC common helps.
Also, improving the risetimes of the Ethernet signals improves things - this one makes no sense at all.
BTW, when I connect the same modded router, fast LPS for the router, fast silver cables and the isolator to my Sonos Connect, it also sounds stellar.
Steve N.
Empirical Audio