Audio Grade Ethernet Cable

Keep your wifi router and  network related wall warts away from your stereo! 

Cheap-o Ethernet 6 will be just fine. 

The most realistic concerns are over radiated RFI from inside the Wifi router.  It's job is literally to radiate radio frequency interference.  The other issue is wall warts.  If you must have any network related gear near your audio gear use low noise versions such as those from ifi Power.  Especially try to avoid putting a wall wart on your clean side of a power conditioner as they can re-pollute the AC. 

If you must do more then I suggest an Ethernet/fiber/Ethernet conversion.  Asus makes routers with built in fiber ports (SFP?) but you can get inexpensive converters.  Fiber is galvanically isolated, immune to RFI/EMI and lightning surges. Still use a good power supply near your streamer. 

As mentioned, you can isolate with fiber, this is very cheap, and effective. I have had good luck putting a Stack Audio Smoothlan in between the router and my streamer. 

@goofyfoot

The easiest and most reliable source for such cables is BlueJeans: https://www.bluejeanscable.com/store/data-cables/index.htm

sns

... how do we eliminate, or at least diminish this pollution source? We locate modem and router close to audio system ...

How does that diminish the "pollution source?" It only puts these noisy components closer to your audio system. 

... modem and router powered via lps ... disable wifi on router in order to eliminate contamination via rfi ...

You can just as easily implement those remedies while also keeping your network components distant from your audio system.

And that’s what I don’t understand: What is the advantage of locating your network components physically close to your audio system? The only benefit I can imagine is that it reduces the length of the one ethernet or fiber cable that connects to the streamer. Please tell me what I've overlooked.

Any Ethernet cable is "audiophile grade" because they all simply transmit ones and zeros. The ones that claim to do that better are either lying or uneducated.