I used PCs for a bit, Mac and Windows. You can achieve good sound. A software program such as Audirvana Plus really helps, because it attempts to shut down the rest of the computer and leave music playing part, as well as providing a GUI to manage your music.
Otoh--it can be a pain switching out of Audirvana Plus when you need to use the computer for non music functions. Frequently I had to reboot several times, which is annoying when you have a task that you have to perform.
If your present computer is still breathing, you may want to use it exclusively as a music server until it croaks, and use the new computer for everything else. However, if I understand the OP, he or she needs a DAC. I would just buy a DAC/Streamer for a few hundred bucks more and get an inexpensive PC. Computers are designed to be obsolete in a few years, and you might have issues with Mac or Windows updates suddenly bricking your PC, then there goes your server. A dedicated streamer is probably more durable and less likely to meet that kind of fate