How can different CAT5/6 cables affect sound.

Apologies, my reviewing of my response was insufficiently critical. I meant to write ... that Google returns is ...

Stereophile_AudioGlossary.pdf

This should be a sticky here on the Audiogon forum!

@unsound yes indeed it should! Thank you for the link, I hadn’t looked at it in I don’t know how long.

Funny, this entry:

Tweak: 1) To fine-tune a system or component to the nth degree in pursuit of perfection. 2) A person who constantly does this in an ultimately vain effort to achieve absolute perfection.

@retiredaudioguy 

Perhaps I am lucky (or hard of hearing) but yesterday I listened back to back to the Weilerstein Elgar from my Aurender SSD, USB connected to the Esoteric K-01XD SE and the same work streamed from Presto through the Bluesound Vault, TOSlinked to the DAC and detected no differences. 

help me understand how this comparison is relevant in a context of Ethernet cable discussion. How’s it even valid at all? 
You’ve heard two totally different streamers (drastically different design) connected to the same DAC using different interface methods, different source and most likely two completely different versions of the master file. I mean no disrespect but it does appear as if you’re hard of hearing. Or there are other factors at play here that negated all possible differences, i.e. room acoustics, setup, circumstances under which this evaluation was conducted (room full of people chattering, windows open with outside noise interfering with critical listening, etc.)

I think it is relevant in that the streaming signal was received through a cheapo Cat 5 cable, an inexpensive streamer and plastic optical link, the other signal was USB from data stored on the Aurender.

I believe that Presto's streaming service aims to provide the same quality of sound as their downloads.

My thesis is that, with a truly well engineered DAC (e.g. The K-01XD with an external rubidium clock), how the digital data gets there is not relevant - given source gear that gets the correct data to the DAC, which all minimally competent equipment and cables do.

Or, perhaps, Presto's MPEG4-SLS codec is more resilient than Qobuz's FLAC, I do not know.  Or perhaps my hearing has gone.

I have been researching the issues and the MPEG4-SLS codec will scale back the quality of the streamed data if there are bandwidth problems.  Those problems could arise if the streaming device detects data errors and causes retransmissions to be necessary, and that could be caused by a poor Cat 5 cable.

Remember my initial question was "how can Cat5/6 cables sound different?", I was not asserting that nobody actually hears a difference.  I guess that the answer could be that the streaming service downgrades their transmission if there are too many data errors.

@retiredaudioguy I am not here to argue with you but it absolutely matters how digital signal gets to the dac. Toslink in my experience is inferior to spdif or USB all things being equal. Different units own clock priority. Digital cables do matter, including Ethernet ones. Even with your Esoteric DAC. 
In addition, your Aurender and BS streamers each have proprietary DSP with Aurender caching the stream onto SSD prior to sending it out to the DAC and BS buffering the stream. Add to that the fact that you don’t know the master files being used from presto and SSD. 
But then again you heard no difference on top of all this with Flac from Aurender vs Presto stream thru BS. Consider yourself lucky.