I also use ethernet rather than USB for the connection to my 140 Pro. USB sounds good but it sounds a bit dull or “flat” compared to ethernet. I have a friend who has a 250 (originally a D Premier) and an Aurender who also swapped from USB to ethernet, I think ethernet gives better sound quality than USB.
As to the noise question, I think that’s tricky. For a start we can’t connect directly with ethernet from a DX or DS to a Devialet because the DX/DS only have one ethernet port so we need to pass the signal through an ethernet switch of some kind, and that switch also connects to the network as a whole. Regardless of whether the implementation of Devialet AIR in Roon makes it non-susceptible to noise, ethernet connections aren’t like a simple interconnect directly connecting a source and an amplifier, they connect both the source (the Antipodes) and the amp to your network as well as to each other via a switch network and switch as well as the Antipodes are potential noise sources. Whatever control Roon and its AIR implementation have on noise, Roon has no control over every aspect of server activity or on switches and the rest of the ethernet network.
The other thing I’ve read is that the noise involved isn’t part of the 0’s and 1’s, It’s noise riding on the electrical connection created by the cable, probably similar to noise riding on your power lines. The noise doesn’t have anything to do with whether you have bit perfect data transmission because it isn’t transmitted in the data, it’s separate to the data.
I’m not a digital audio expert and I have little knowledge of all of the issues supposedly involved in digital audio. All I know is that I find it easier and simpler to run a server located in my listening room next to my amplifier than to use my Mac Mini as a music server in addition to it being my desktop computer and I’m getting better sound quality with my DS than I was with the Mac Mini. I can’t see myself ever wanting to go back to using my desktop computer as my music server.