As folks have pointed out, the issue with the question is the word audiophile. No, no chance this will happen for either $2,500 or with a PC involved. Doesn’t mean you cannot get enjoyable sound out of it. I enjoy my office system.
Given his current system was a Microsoft OS based machine, I would doubt he now wants a MAC. I would never buy a used PC. If open to a Mac book, you can run it on batteries, which I used to do for my streaming (sounded terrible compared to any real streamer).
But you can get decent sound out (enjoyable to listen to) with a good sound card, lots of power conditioning, and good amplification.
So the real question for OP is has anyone a PC recommendation? I have a huge tower that I made, 14TB, water cooled, but very expensive. With all the space inside it sounds OK for my office system.