Moved Audio Quest cable to my DAC. WOW

You have  Mac 452 and that's now mid? My how things have changed. Had a pair of MC 275s in '85 same happened . Kids with college degrees now. Back down the rabbit hole!

I, too, had a similar experience with my Aries Cerat Helene DAC, but it was not the PC; it was the interconnect (Nordost Valhalla 2 XLR). I do, however, power the AC with an Audioquest Hurricane PC. The addition of the Valhalla 2s between my source and McIntosh C2700/MC611s was immediately apparent with the highs. McIntosh is known to be a little restricted on top, but no longer with the Valhallas. I was skeptical that the source cabling could profoundly affect the system. I always thought the preamp/amp connection would make the most difference. Boy, was I wrong!!

An excellent power conditioner with shielded power cables to all equipment are highly recommended. It's nothing to do with electrical engineering, but EMF contamination of the power cable between the conditioner and the equipment. Its probably only audiophiles who are aware of this phenomenon.

It’s a curse having an electrical engineering background. It holds you back from getting a great sounding system. You think too much about things, using that hard-learned logic to persuade yourself that things can’t possibly work. I was similarly afflicted, but have now learned to listen first, then having decided if the difference is there, and is tangible and worthwhile, then use that engineering background to work out what’s going on - how can that work? You have to think outside the box too.

I have a much better sounding system now, and better understanding of what matters.

Wait till you try Shunyata, with one of their power conditioners…