Quality of digital cable from from source to DAC?

Lots of opinions on this subject but, as with any other cable debate, the only conclusion that matters is yours, based on what you hear in your own system. Even more than with other analog cables, opinions regarding the relative quality of different RJ-45 cables seems to be a crapshoot.

The range covers those who believe there is absolutely no difference in digital cables (i.e., the zeros and ones crowd), those who hear differences but not necessarily sound quality "improvements" to the level that justify spending a lot of money on RJ-45 cables, and those who are all-in on the value of expensive, purpose-built (i.e., boutique) Ethernet cables.

Nobody here can make your decisions for you and what you read could be (and often is) very different than what you will hear in your own system. The articles and reviews I have read support a pretty wide range of solutions, including:

• improvements being gained by simply replacing your Cat 5/6/7 cables with (slightly more expensive) Cat 8 cables,
• further improvements resulting from a range of lower to mid-priced network cables ranging from the relatively inexpensive Supra CAT8 Ethernet Cable or Viablue EP-7 CAT6A Network Cable, to the mid-priced Wireworld Starlight Cat8 Ethernet Cable, to something a bit more expensive like the SOtM dCBL-CAT7 Audiophile Ethernet Cable, and then
• the need to spend money on relatively expensive, esoteric network cabling to get the most from your digital gear, such as the over $1K J- CAT Ethernet Cable or the uber-expensive AudioQuest Diamond RJ/E Ethernet cable.

So, you asked for some links. Here you go. The first link includes a discussion of "blind" testing the author conducted. The other links are mostly reviews of the cables mentioned above.

http://www.audiodrom.net/en/special-edition-reviews/104-ethernet-rj-45-cables-shootout

https://hifiwigwam.com/forum/topic/132474-throw-away-your-ethernet-cables-and-audition-some-cat8-ethernet-cables/

https://audiobacon.net/2017/05/31/supra-cat8-ethernet-cable-review-an-amazing-spotify-and-tidal-experience/

https://www.audiostream.com/content/wireworld-starlight-cat8-ethernet-cable

https://audiobacon.net/2017/03/16/sotm-dcbl-cat7-review/

https://audiobacon.net/2019/12/06/jcats-1100-ethernet-cable-now-with-gold-connectors/

https://parttimeaudiophile.com/2015/07/24/audioquest-diamond-vodka-and-cinnamon-ethernet-cables/

http://www.the-ear.net/review-hardware/audioquest-ethernet-cables-pt2-ethernet-cable

https://arstechnica.com/staff/2015/02/to-the-audiophile-this-10000-ethernet-cable-apparently-makes-sense/

Thanks everyone for your time and effort given.

Twoleftears, waded thru some of the silver/copper discussion and remain perplexed (as I believe was your intent to display I am certainly not alone) that little mention was made to the differences (if any do exist?) in the movement of digital signals vs. analog signals.   
Wow Mitch, thanks for your input and effort with all the relative links. No doubt to be intriguing reads.

I will be letting my ears and wallet that will determine MY take on this. Am comfortable knowing that some things in life (for which this may be another instance) simply defy explanation. But my desire to have understanding of most things is strong, particularly when they effect both my happiness and my wallet. Wish it were easier to do some blind-tested cable swapping myself, but for numerous reasons this is not likely to ever happen. Too many hobbies and desires. So just trying/hoping to make the best out of learning thru others reported efforts and experiences.  

Have had opportunity to acquire several credit hours of physics, thermodynamics, etc. in my earlier years. While I can't necessarily hold an in-depth conversation on ALL the various aspects involved as electricity passes thru metal, I do have at least a little understanding of that physical process and many of the factors/elements that might affect it.

Hoping some of the links offered might delve into the differences (if they exist?) between the movement of digital data vs. analog data thru metal cable runs. This I have little to no understanding of.   

ecolnago
Have had opportunity to acquire several credit hours of physics, thermodynamics, etc. in my earlier years. While I can’t necessarily hold an in-depth conversation on ALL the various aspects involved as electricity passes thru metal, I do have at least a little understanding of that physical process and many of the factors/elements that might affect it.

>>>>Don’t be shy. Please share. I’ve been trying to get just that, an answer to the dodgy question, “what is the audio signal,” for some time.

Like I said before, show me in operation some optical glass fiber RCA interconnects, and we can start to conflate the discussion of analog and digital transmission.