I’ve never heard of two computers “syncing” iTunes. Copying libraries perhaps but syncing?
In the beginning the Mac was the “mothership” and the iPod was the “shuttle” (think Star Trek). The content (first music, later video) was stored on and playlists were edited on the Mac and then uploaded to the pod so you would have all your entertainment in your pocket. That was when iTunes was in its “buy and download” phase.
As iOS devices gained more functionality the whole concept of “syncing” became irrelevant to most people who preferred to download content directly to their iPhones. Then came iTunes in the cloud and the content isn’t really on your device anyway.
So what is it you’re trying to do exactly? How are you connecting the PC to the Mac?