the question of changing ethernet cables

Many thanks. I understand the issue better as being 2 distinct loops, shall we say. The problem I wish to solve is twofold: Firstly, now that I have the hardware, I wish to optimize the cabling and refine the system (mostly Cardas XLR). Secondly, I have a white noise (?) at the higher mids or from the mid range driver (Speakers Focal Sopra III).

To begin. I had Furutech fuses (Sicherungen) connected to the fuse box and Furutech outlets at the wall. These are 2-separate lines with 6mm2 (10 Guage) wiring. These are dedicated lines with no loop at all - direct. One line is just for the amp (PS Audio 250 sig) connected to the wall with a Shunyata Alpha NR. This has been a game changer.

I have read here and on other posts that the router and ethernet cables can induce some noise pick up. The first question has been answered; namely, despite the fibre hook up coming into the house, yes, noise can come from internal parts thereafter.

I am very impressed with Shunyata and I will look into their ethernet cable. I also saw a video and post about green computer or something like that using filters and adapters from ethernet to fibre connections. I believe the remaining hiss or white noise is coming from the router. I am almost ready to try this remedy. I just needed to clear up my quaetion. Lalitk and antigrunge2 sound like they are leaning in this direction. My plan would be to try this first and later, if necessary to replace the ethernet cable.

Oh, if I have just the amp and preamp on I have a very slight hiss, volume turned up and ear to speaker or just some inches away. When I turn the streamer on the same noise increases. I would like to have dead silence if that is possible. So, my plan is go one step at a time to reduce as much of this hiss as possible.

@finnlove 

From your description I would guess that the problem actually stems from your router: do you use it for wifi? Can you turn wifi off? Can you use a linear power supply for the router? What model do you use; can you try to upgrade? Also try a Lan isolator, my preferred solution is Pink Faun. Alternatively EMO or Acoustic Revive work well, too. 

RFI/EMI does normally not result in white noise since it happens at much higher frequencies and modulations at that frequency range would be very weak. More likely this is noise coming from the router‘s power supply.

Thank you antigrunge2. Everything is in the attached garage, modem, router and this station system to extend wifi. Meaning the main station extender and the slaves are positioned around the house for better wifi.

The router is plugged directly into my fuse box. I have outlets built in. I can see from the wire pile up and the proximity, as well as the use of, the fuse box could add to the noise.

I just started to read about your suggestions. Pink Faun is produced in the Netherlands, which is very close to me. There is also a dealer I found in Germany. It diffently sounds like I need to add some type of filter post router and a filter converter to fiber. Then a fiber cable to the streamer/DAC. That was green computer's solution as I understand so far.

As I said, I am still looking at Lan isolators. I do have to say, this is quite an interesting science. 

“I have just the amp and preamp on I have a very slight hiss”
@finnlove

I suspect that white noise / hiss your hearing is coming from router. Without knowing every single component in your system, we can only speculate. I used to own a tube amp that produced a very faint hiss, I could easily hear it when I am near my tweeter but otherwise inaudible few feet away. As you said, hiss is already there when you turn on amp/pre. The noise is further amplified when you turn on streamer. I would look at each and every step in your signal chain i.e. interconnects, speakers cables including LAN cable.

Before you drive yourself crazy and spend more money, do you know if your electronics are supposed to be dead quiet? Contact the manufacturer or read other users feedback. Are you using a power conditioner in your system?

The most common reasons for hiss is poor grounding or gain stage in your preamp. It could be also from poor wiring or EMI/RFI in your environment.

+1 what @lalitk and ​​​​@antigrunge2 Said. The entire chain is key. Quality cable with quality shielding, isolation, quality modem and switch.