Quality of digital cable from from source to DAC?

Hoping just to gain some understanding.

With respect to the transfer of digital data via metal cable in the audio spectrum, the seeming common thought I’ve managed to discern thus far is that while there is likely no apparent SQ differences to be gained in upgrading the quality of my Cat 6 ethernet cable that link my router (ATT Optical feeding an Apple Airport Extreme) to my streamer (50’ run of off the shelf Cat 6 feeding a Lumin D1), there seems to be considerable reviews claiming significant SQ improvements to be had in utilizing ‘higher quality’ digital cables linking the source (streamer or CD transport) to a DAC (Qutest). Why would this be? Is the digital data file going from the router to the streamer somehow different, or more suspect to error, than the digital data file going from the streamer to the DAC?

Any insight would be greatly appreciated, even if nothing more than passing a long a related link.

Thanks,
Todd