@jay73 Let me tell you my setup. Maybe my explanation will answer your questions.
1) I have 5 PowerLine adapters hooked up in 5 rooms of the house, including garage. These PowerLine adapter are $50 for a pair and transform the copper wire in your house electrical wiring into an extension of a homes Ethernet network.
https://www.amazon.com/gp/product/B00AWRUICG/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=12) I have a cheap DELL server ($400) that is running ROON Core in one of the rooms in the house. I do not think it matters about the internal electrical noise in this computer (explain later). The computer is connected to my Ethernet network using the PowerLine adapter. I have not used JRiver in a few years but if JRiver could function as a server then you would install that on a dedicated server like I have.
3) I have 2 audio systems in 2 rooms with 1 hooked up to the PowerLine adapter (living room) and the other hooked up from a network switch connected to my router (office). The other 2 PowerLine adapters are in the garage for my business servers and the family room for a MacMini for YouTube etc...
4) For the audio system in the living room. I connect an Ethernet cable from the PowerLine adapter to a microRendu in the living room. The microRendu then is connected to my DAC by USB. Now in the future, with available funds, I will change the microRendu to an OpticalRendu because the OR is so much better. However, instead of using a Network switch (which I could still use) I will likely buy the OpticalModule from Sonore that can convert Ethernet input to Fibre (similar to a switch). The reason for maybe not using a switch is to avoid flashing lights from a switch.
5) In my office I have a network switch (with flashing lights) that has 2 Fibre cages installed. I take 2 Fibre cables from the switch and input them to 2 OpticalRendu’s in the office system. The OpticalRendu’s then connect by USB to my 2 office DACs. I do not need the OpticalModule to do any Ethernet to Fibre Optical conversion. The switch already provides me Fibre.
For my music playback I use the ROON client that I have installed on my iPhone, MacMini, and a PC that is not my ROON Core PC. I can wireless control playback if required.
The beauty of the Optical is that it sounds amazing and I am told the reason for this is that Fibre cannot transmit analog electrical noise into a DAC (very bad) hooked up to an Ethernet network via RJ45 or USB. Noise can include power supplies, RFI, computer noise, etc. The Fibre is supposed to stop all that and will transmit a clean signal to the OptcalRendu which may add a bit of noise since it converts to USB.
The only DAC that I know of that can take a direct Fibre Optical cable as input is the Lumin X1 ($15K). So I will stick with my $1500 USB DACs which I feel using the Fibre Optical approach I have described is much better than RJ45 streaming and the microRendu.