Hard to believe all the crap that flows thru an ethernet cable


So apparently lots of crappy stuff needs to be cleaned up from your ethernet cable before reaching a dac.  
And to thoroughly clean it up you are wise to spend $1300 for an optical rendu device, and sound quality drastically improves.  Wow. Sounds like a great deal.  
I guess a really good dac with galvanic stuff going on and strong pwer control needs more help.

do i really need a rendu device? I see it on high end systems so that seems good.
jumia
You think that's bad, you should see all the crap that flows through my internet connection.
AFAIK galvanic isolation is built into Ethernet standard (transformer or optical), but any additional isolation might help.  It would be wise to try before spending money. 

DAC designers would likely use transformers, since they eliminate DC and suppress common mode electrical noise (and are cheap).