It’s too bad that the OP didn’t even check out his 375 before the 60 day return window(pretty long return window). Always at least check out your new component before the return window, people. It’s no comfort to the OP, too bad that things turned out so poorly.
I had a C356BEE with the dac unit installed, and I never attempted to connect a laptop or computer. When I sold it the buyer said he was getting some hum when he connected his computer. I did a quick google and found some cures on the hum. I forget what I found then, but perhaps it’s an easy fix. My buyer was able to find a cure on line.
I wasn’t too impressed with the built in dac, however. I’d advise the OP to get a cheap stand alone dac and forget about the Nad one, it’s a dud compared to what’s out there for cheap these days. I’d suggest a Schiit Audio Modi 3 for $99. It’ll surprise you what you’ve been missing in your music.