Two way sync a single folder between two Macs via local network
I was in a very similar situation a few years ago. I had a Mac mini and a MacBook. While the Mac mini contained all the tracks I wanted to use the MacBook like a giant iPod (sync star ratings, renamed songs, etc.).



Solution: iTunes Match (music only)


Subscribe to iTunes Match on your main iTunes Library.
Wait for iTunes to upload/verify all unmatched songs in your library.
On you other Mac, turn on iTunes Match.
As soon as both libraries are updated, you can change a songs Metadata and it will sync over the internet.


Note:

It's a bit of a pain in the neck to wait for iTunes to upload all unmatched songs. But once that's achieved, it works like magic.