@hilly230, Glass is better than plastic for Toslink... Coaxial is susceptible to RFI... Wifi may give you some physical isolation at the cost of increased RFI... Ethernet cable is pretty clean at cat 6 and above...
I use Wifi to/from my laptop to my local router, wired ethernet from the router to the streamer and USB to the Qutest which has galvanic isolation plus some other trix Rob Watts designed in...
For testing, and to be fair, I would turn off all MQA processing in the Node and use known quality and resolution source files to compare the two DACs... I, and many others, are suspicious of any source material from Tidal now a days...
I also wonder if your amp is doing something to the signals... Maybe digitizing the incoming analogue for further internal processing?