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.