Network Switches

Before I go looking at a switch for issues, try looking at all the cables and connectors first, then if you are using copper for your outside network, change that to fiber. When I did corporate networks in the early 90’s, we would verify/signature every cable we would make with a fluke meter and a good number of them had to be reterminated because of too much noise. Also, most home network cables are terminated using the cheap plastic ends. In my house, I use a 1G fiber to the outside (probably much more important than any switch because the lack of noise), and cat 7 cables to my audio and server components. 

I just got Silent Angel Bonn N8 switch from Crux Audio USA ($399.00) The difference in sound quality was shocking, it was like listening to a new much improved system. A couple of reviews:
https://www.lexicommultimedia.nl/review/silent-angel-bonn-n8-ethernet-switch/
https://www.hifi.nl/artikel/28188/Review-Silent-Angel-Bonn-N8-ethernet-switches.html

A month ago, I purchased a new streamer as I was certain it was the weakest link in my system. I had previously been using a Sonos Connect modded by W4S.

The Sonos Connect allows you turn off its internal WiFi module if using ethernet. I found this gave a slight improvement in SQ - and confirmed to me the benefit of reducing electrical noise in your digital chain and components.

I use the Netgear Powerline devices to get ethernet to my streamer. Based on the status lights on those devices, I was linking at less than 50mb/s, and sometimes I would completely lose the ability to stream 16 bit FLAC files - dropouts, lost link, etc. That’s only, what, 1.4 mb/s? Very frustrating, but with the Connect, I could just switch back to streaming via wifi.

The digital chain is:

Router -> Powerline adaptor -> wall sockets -> Powerline adaptor -> streamer -> DAC (spdif)

My new streamer does not have WiFi. I had to solve the powerline dropouts, and I also wanted to reduce noise in the chain as much as possible to get the most out of my new streamer (which was immediately a major upgrade in SQ over the Sonos - even with my finicky and poor networking architecture).

I changed out my router from the Comcast router to a Motorola. My wifi performance improved, but the ethernet issues with the powerline adaptors did not. I then switched out the stock SMPS on the router with a Sbooster LPS, and replaced the unknown/stock ethernet cable with the Blue Jeans cat 6a. The powerline adaptors were now linking at 100mb/s with no dropouts and I heard improved sound.

Steve Nugent from Empirical Audio suggests "fast" LPS for routers, switches and streamers - anything digital. He stated the Sbooster was "fast", so I went with that one. I think this might be related to the power supply "pumping" injecting noise that @atdavid has brought up. I don’t know, but I do know this change helped.

I was reading about audio network switches as a upgrade (to be deployed between downstream powerline adaptor and new streamer). I was having thoughts similar to @almarg in that, as he stated better than I could:

"differences in waveform characteristics in turn may, IMO, affect the degree to which some of the RF energy present in the signal may bypass, i.e., may find its way around, the ethernet interface circuitry in the receiving component and affect circuitry that is further downstream".

Knowing the powerline adaptors were probably noisy as heck, going the switch route seemed like it would be less effective than isolation. So, I decided to buy the Gigafoil v4 ethernet filter - basically a ethernet-to-fiber-to-ethernet device that removes potential noise on ethernet cable.

I’ve powered the Gigafoil with an Sbooster LPS, and connected it to the network with a Blue Jeans cable on input side, and a higher end cable on the output to my streamer.

The results? I totally concur with @parsons previous comment: tighter and more realistic base, lower noise floor, relaxed, dynamic and I can listen to it out much louder volumes comfortably.

I have a power cable for the new streamer on the way, as well as a new coax cable. Hopefully, those will be that last upgrades for a while.

Sorry for the length of this. I wanted to share some recent experience related to this topic. I totally agree with @grannyring :

Everything matters in our digital audio front ends. Everything folks.

@mitch2

To make sure I am clear, should I run a single short Ethernet cable from my router to the switch and then connect the various TV devices, plus my Antipodes DX server, to the switch....is it that simple?

Yes correct. It doesn’t matter if the TV is connected to the router or the switch. Just the audio components matter.
The reason I suggested a second hand Cisco 2960 switch rather than a cheap new net gear switch is that:

1. When compared to a cheap switch they sound better. I compared the Cisco 2960 to a cheap net gear and the difference was obvious. The Cisco switches are really well made and have top quality parts inside re clocking, power supply and shielding which seems to help compared to a cheap new switch. 
2. I have heard that they are comparable to an audio switch but have never heard a dedicated audio switch so have no evidence here. 
3. They are cheap on eBay. In the UK a £400 new price 8 port Cisco 2960 switch is £50 on eBay. 
4. If it does not work you can resell it for the price you paid.

Thanks again guys.
Regarding power supplies, I have an HD Plex just sitting around that I can hook up to my router this weekend.  The HD Plex I have is totally configurable for different voltages with multiple fixed and variable outputs.  I can also verify the output using my volt-ohm meter.  I may eventually be able to use it to run both the router and a switch when I get one.