Brave man John to tackle this subject. Like yourself I have an I.T back ground but like so many areas in audio you need to listen for yourself. I found even a entry level chord ethernet cable made a wothwhile improvement. Once again a great video, congratulations.
Two quality network switches with SFP ports will do the same for $200. - get a 48 port Switch and space out your cables 300mm instead of 30mm - use one network switch for your home network and connect your switch (dedicated for audio) to the main switch with FIBER Also, a quality multi-rail power supply you can not fit in this small box.
Sorry but if your multi-thousand dollar streamer is letting signal noise from an ethernet port get to any of the analog circuits, it's simply shit. If this was in any way a problem, those high-end streamers would offer SFP ports for fiber-optic connections. There is no way that ground-induced noise can travel over light. As you know, most SFPs now are LED driven (not laser) and will not induce any noise themself.
John, like your self an electronic engineer, wonder if there is more hype around switches. That said why went over GE, Myra products? Good presentation Station, I assume the biggest leap may be PSU elimination of noise been transmitted into the unit🎼🎵👍
ISP routers are generally 'functional' low cost items... so we are 'insulating' the audio system from the ISP router by feeding it through the QNET. If the actual quality/speed/bandwidth of the broadband is low then the QNET won't do anything to improve that (e.g. when playing from Qobuz, Tidal). The QNET is all about reducing noise and improving timing of the data connection into the audio player.