Network Acoustics Eno Streaming System vs SGC Optical Isolation System

Total noob with this side of stereo and streaming, so hope I don't annoy anyone with simple questions.

Is it better to have both the cable modem and the wifi router as close to your equipment as possible, or should the two be separated some distance?

I've always had them next to each other in the basement, and mainly use wifi but I want to move towards wire cabling from basement to the stereo (ethernet?) and then contend with it from there. 

Thank you @charles1dad for the response, and other replies.  Learning a lot about the 'in house' side of getting things best established for streaming.

I typically use wifi to stream from computer to Black Ice FX DAC, or to a Chromecast Ultra HD puck to stream audio and video to TV; and then thru Toslink into the DAC. I am wondering if I should be moving the cable modem closer to the audio system, (it's like 3-4' away) and then using the Ethernet out to the Chromecast Ultra which has an Ethernet in thru their power adapter (odd, I know).  I 'feel' like I am getting some very high end glare or high frequency sort of whistle regardless of streaming method or DAC, leading me to wonder if it's from the wifi/modem/cable integration to begin with?  

Very helpful info about the ground loop potential with distant set ups.  That made a ton of sense.