Ethernet

I’m fortunate that my router is about 6 feet away from my streamer. Fortunate because I live in a mid-century ranch with aluminum siding. My home is where WIFI comes to die, multiple mesh units and all. 
I don’t know if I can hear the difference, but in my case, a cable connection is preferable due to bandwidth and dropout issues.

After running Ethernet to all my equipment I also employed one of these iFi/Silentpower LAN silencer devices. I put it between the router and the first switch in my chain.  It works as advertised and made an audible difference in the system.  
SilentPower LAN Purifier Pro

The answer is "it depends."

I have a Powernode in a second system that I ran wirelessly for a while. The router is in the same room. I decided to run a Cat 6 cable from the router to my Powernode and the sound quality got worse. After doing some research, a plausible explanation is that most routers are cheaply built and can introduce noise into the streamer. I recall seeing a streamer manufacturer being interviewed and saying that wi-fi is preferable to cable for this reason.

I wanted to hard wire a TV in the room, so I inserted an ethernet switch and ran cable to the TV and to the Powernode. The sound quality seemed to get better. Then I tried the mod of inserting media converters with a run of fiber optic cable (discussed elsewhere in this thread). and the sound was restored to what I was hearing via wi-fi.

I suspect a number of things can affect the wi-fi versus cable sound quality - the build quality of the router, the build quality of the streamer and it’s ability to filter out noise and interference, how strong your wi-fi signal is, how many other wi-fi signals are in your area, etc. etc. 

So, after hearing the big improvement in the sound quality of the media converter mod, I decided to try it in my main system. It seemed to make no difference.

Which gets me back to my initial answer - it depends.

My connection from server to DAC is about 25 feet, and runs past or along mains power cables, speaker cables, and interconnects. I was never able to get better sound from copper than from WiFi. 
Saying that better cable will be better than WiFi is nonsense. It all depends on your set up.

I finally got the best sound using fiber ethernet. I started with using convertors at either end, and wound up with an Optical Rendu connected directly to an optical out on my server.

@maprik there are a number of discussions on these forums and elsewhere on the internet about differences in streamers. There are various factors that influence some of the differences. You can search and read up on it. Or you can use chatgpt or gemini or grok and you’ll get a nice summary based on what these models were trained on (data from online forums, eyc.)

DDC is not a cure all. These vary in quality based in design. One of the key differences is the clock that’s used internally. With DDC, however, you introduce additional cables and potentially additional source of noise - EMI, digital and AC, that needs to be dealt with by the DDC, DAC and other components plugged into the same circuit.

Add to that the i2s connection that’s never been designed for connecting external components and has no industry standard when it comes to pin configuration. 

Back to your 25ft run of Ethernet cable - you are adding a source of noise that your Node, DDC and DAC will need to deal with. Like I said try it. 
I’ll be on a lookout for your next discussion about LAN isolation, Ethernet filters and fiber optic conversion. Good luck!