Network Switches

I would like to know why I would need a switch as discussed here, where I would use it, and what it would do for me.

@mitch2 
Buy a cheap second hand Cisco 8 port switch from eBay and connect it via Ethernet to your router. Connect your streamer etc to your network switch rather than directly to the router.   The result may surprise you. 

@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.