The same way you wrote - use NAA.
Trimmoy Amethyst → SPDif AES/EBU → “magical device/DDC” → NAA → ethernet → Antipodes S40 with HQPlayer installed
This NAA can be a simple Raspberry Pi 4 running NAA OS from Jussi’s website.
I wouldn’t worry about that. That is from RME user manual. The engineers at RME are pretty good 
If they say it is compatible with AES/EBU, given their pro audio / studio pedigree, they know what they are talking about.
You will have it network isolated anyway - you just need bit perfect transfer to the NAA, nothing more/less.
But if you can afford a Pro model (you will be paying for both ADC and DAC and not using any of it?) then Pro model is the way to go.
Btw, what is your chain after the Antipodes? What NAA and what DAC?