Quick DAC question

through any digital output on the Oppo 105 means the Gustard is the DAC stage

You did not specify digital RCA, but singular we assume the RCA is a digital out of your Oppo vs a pair of RCA analogue out.

And yes, digital out means the next unit has to be the DAC,

I know I should run a physical ethernet cable into the gustard and just use the Oppo as a CD transport but that's going to be a last resort because of the location of my modem / router way down in the basement.

There’s an easy solution for this — just get a Wi-Fi extender or Mesh system and run an Ethernet cable from that to the Gustard.  Many people do it this way with great results and not expensive. 

@soix That's what I do.  My internet comes into the house on the main floor.  My system is in the basement.  I use an ASUS wireless router to send the signal to the basement. 

It's a good router.  I rarely have any issues with wi-fi. 

+1 soix. There are extenders like soix mentioned and there are ac line adapters. They both have an endpoint unit that you can plug in at your system and run an Ethernet cable from that point to your Gustard thus eliminating the Oppo in the chain. Then get a short high quality Ethernet cable and connect the 2 points. In my case I run an Ethernet cable from my endpoint to a LAN filter that’s sitting on block of wood for isolation and then a 18” higher quality Ethernet cable to my streamer.