I've got to run out now, but I don't know how this "light link" works -- looking briefly at a vendor website as I don't have the time to look into it further right now, but it look like they are referring to optical cable. So, it seems like you are not limited to using it between a NAS and a DAC, but you could use it between a PC and a DAC (I'm guessing here but I take it distance is an issue?)
So without knowing I'l just put this out there
Think of the NAS not as a server but just as a big external drive for your shared media. Then you have a "media server" (JRiver) a "controller" (JRiver and/or JRemote) and you want JRiver as a "Renderer" (the player if you will). Right now you are only using JRiver as a controller or maybe as a media server and controller (not sure)
AS you are already cabled with ethernet (gigabyte network?). WIthout knowing any details or constraints due to your room/house etc. What I would do is connect the NAS via ethernet to the PC with JRiver on it acting as a server (you could have multiple PCs/devices as clients too; JRemote could also become a client btw). Then you connect the PC to the DAC directly (you can use SPDIF optical out if you want). Doing it this way you get the best of everything because JRiver is acting as renderer and server. You have a fast connection via ethernet from your NAS (absolutely no quality loss - if the network is very slow, you might have issues with lags for video).
I can't tell if this "light link" is even necessary, unless your PC only has a USB output (I don't like USB cables longer than 1 meter, actually I don't like USB connections at all if I had a choice
but thats just me!)
AS for you number 2, the sound will be no worse, and almost for sure will be better ...
because JRemote is the renderer. An ethernet connection to your PC is fine (even newer WIFI connections can be fine these days) - JRiver does its magic after that. There are other benefits of setting up this way.
The important connection is between the machine with JRiver on it and the DAC -- the choice of what type of cable depending on your DAC inputs, distance etc. and personal preference to a degree -- some people like HDMI for multi-channel; I prefer optical over coax if its a long connection, but I'm no engineer (I'm not a believer in spending fortunes on cables either
Maybe a little more specifics on limitations imposed by your room layout and some info on this light link thingy?