Ethernet Cables, do they make a difference?

@markalarsen - no baiting, trying to understand your configuration and what you imply by "Ethernet connected to DAC"
From the "Bel Canto" web site:

The Black EX Integrated amplifier is an all-in-one component designed in a custom plated high-grade aluminum chassis that combines high-level DAC performance and our custom amplification. The EX Integrated has the versatility to connect to any source with simplicity and ease, including MQA, Roon, DSD, and includes an internal programmable phono stage.

Key work is "All-in-one"
Device above combines many components in one (from the Ethernet cable to the analog output - simplified):

• RG45 connector
  
• Network card
  
• Memory buffer
  
• Media player
  
• Digital to Analog Converter itself
  
• Analog sound circuit
  
• Analog output plugs
  

Do not get me wrong - I'm not questioning quality of it but...
With so many components combined in one unit there are a lot of possibilities to get noises produced by digital components in the analog ones.
Bad or even wrongly designed shielding of the Ethernet cable can produce audible effects so much spoken above.

High Audio quality Ethernet cable may show poor performance in the data centre where throughput is important.
High Network quality Ethernet cable may show poor performance in the audio system where no-noise is important.

Both sides in this discussion are right! Period!

I shall say it again - each setup is different!

Mine performs the same on Cat5 and Cat<a lot> because... (drums)
Ethernet cable delivers data to computer, computer runs media player, media player buffers input and sands steady data stream to DAC over the optic cable or USB cable.
Optic cable facilitates that electrical disconnect in digital chain below DAC.

clearthink - There are 100’s of posts in that thread just tell us hear what you mean by "ordinary speaker wire" and if you are open to other participants in the challenge perhaps willing to meet your $25K USD to attract more participants.

@clearthink

No need for you to continually write "$25K USD". I think everyone knows by now 😆

By the way, at the rate we’re going, I’ll need to tack on interest. 😅

To your question about ordinary speaker wire, refer to this article and search for "ordinary".

http://www.roger-russell.com/wire/wire.htm

Basically this means you and I can walk in to home depot and ask the rep for wire to fix a table lamp. Something like this:
https://www.walmart.com/ip/Pyle-18-Gauge-High-Quality-Speaker-Zip-Wire-50/20551674?wmlspartner=wlpa&...

@grm

Please accept my apology for the off-topic communication. 

If one thinks noise is an issue, they can and should test for that. Whether they think the problem is noise getting inside the ethernet cable or the noise getting out of the ethernet cable.

I personally haven't found noise as discussed above, to be a problem in my setup with my Bryston BDP-1. I use an 18 feet AES cable so I can move the BDP-1 far away from my rack so no ethernet cable goes near the rest of the components. I don't notice a difference when the BDP-1 and the ethernet cable is in the rack or far away. In fact, I've tried piling 100 feet of Cat6 UTP on my DAC and interconnects, and noticed no difference in sound. I suppose my interconnects and gear is well shielded. It very well may make a difference in other people's setup.

Similarly, I can play music off a USB flash drive, and use the ethernet connection for only interface control. I don't notice a difference in sound by the plugging and unplugging of the ethernet cable. If there is noise present, the unplugging of the cable should make it better.

However, I do find a difference when streaming through Roon based on the length of the ethernet cable or the device/power supply used. Based on my experiments, I haven't been able to find conducted and radiated noise as an issue. Aside from shielded and grounded ethernet cables which are breaking the isolation, I suspect in a calm home environment, the differences in sound may be with how the signal is dealing with the PHY. Signal integrity could be at play here.

It's hard to conclude anything without measurements, but still there are tests that people can do at home to test out various hypothesis.

@zoom25 good explanation is here: https://www.stereophile.com/content/bryston-bdp-1-digital-audio-player

If player and DAC are separated Ethernet cable should have no influence