Ethernet connection for best sound quality

Any CAT-5 is fine. All this "audio grade" is pure snake oil. I say that because being a computer systems architect and system admin, ( retired) I know how Ethernet works.  You see, there are these things called "packets" that are buffered and assembled.  Now it is possible to get noise and ground loops over Ethernet, but that is solved by proper practice, not magic. Use shielded if for some reason you have very long runs in horrible environments. Doubtful.  In the data center world, we use fiber to totally eliminate noise and ground loop issues.   Now, as far as errors, TCP/IP will correct any error. Absolutely 100%. If running UDP, then you could get a bit error in the transport layer, but an application layer if well designed will detect that.  You would be surprised how much traffic goes around the world, sat hops and who knows how many switches in UDP with no errors. 

I disagree with "streamer vs PC" as a blanket statement.  Sure going through the Windows audio stack stinks, but ASIO or WASAPI-exclusive, asynchronous with the server configured at - 3dB so the oversampling and filters do not cause digital clipping and a sufficient buffer,  then bits are bits until they reach the DAC.  One can even set the process priorities so when Microsoft decided upgrades are the most important thing in the world, or McAfee takes over the Kernel, then you can get prevent a skip.   To say all streamers are better than all PCs is nonsense. There are some crap streamers out there.  There are some very very good ones if you can stand the tiny UI. 

Yes, USB was designed for keyboards and mice, but they have beat it to death over 20 years and it is now very good.  Don't hold biases that are obsolete.  Computers putting out PCM put a lot more of the issue to manage jitter on the DAC and there is no buffer. You are basically real-time from a source that is not a real-time operating system or IO.  USB and IP solve that. 

yage

I don’t think the average audiophile realizes that these multi-thousand dollar products are based on low-cost, low-powered hardware and freely available open source projects.

You seem to think you possess some special knowledge. I think the typical audiophile buying a multi-kilobuck streamer knows very well what's he's buying. Most likely, he also listened to it before purchase, and it's also common to buy with a return guarantee.

The fact of the matter is that a great sounding streamer can be made from something as simple as a Raspberry Pi 4 ...

That is very true. When I first started streaming and wanted to graduate from using a phone (hey - we all start somewhere!), my first stop was a Raspberry Pi with a HAT to a digital out. It worked like a charm into my Bryston BDA-3 and I can certainly understand why some audiophiles might stop right there, just as some users might have stopped at using their phones to stream. Many people are satisfied with that level of performance.

@tvrgeek 

https://cdn.shopify.com/s/files/1/0660/6121/files/UpTone-J.Swenson_EtherREGEN_white_paper.pdf?v=1583429386

For the umpteenth time: Bits are bits but all audio is analogue!

Do we have any CEE’s out there? The shielded cat 5e, 6 or 7 cables makes perfect sense. Installing high quality connections is also a no brainer. However, reading this thread brings up a few interesting questions. What internal components and design concepts are being utilized in high end streamers, like those previously mentioned? Since I own a Lumin U2 mini, I will pick on it. Has anyone with a CEE degree analyzed its design, construction, and components? Other than sound quality, which is extremely important, this is where the rubber meets the road. What do you see under the hood? Is it a Ferrari or a Chevy? The same question would apply to any other high quality streamer on the market. 

Actually, "digital" is a mathematical concept. There is no such thing as digital in the physical world. 

But in the  transport area, bits are bits.  What you do with those bits is where the differences in sound come from. I might suggest a review of the IP stack and some basic systems understanding would enlighten some readers here. I only have over 40 years CS experience so what do I know?  :)

Above CAT-5 is ridiculous for audio.  You are not building a 10G system. CAT-3 is fine but having the pairs with consistent twists and bonded as in CAT-5 is good practice. Most consumer grade Ethernet hardware does not even have provision for the shield ground.  Look at the socket. If it is not plated, then shielding is useless.