Well…I could tell you how to move the other way 
- Make sure that empty trash during each scan is NOT enabled.
- Install plex on Windows, and shut down Plex on both devices.
- Copy the whole darn Library directory from QNAP to Windows, replacing the existing one.
- Power up Plex on Windows
- Go into each single library section, and add the new Windows path to it, so both old and new are present.
- Refresh each library section
- Check that all movies etc. are now doubled, and one is avail, the other missing.
- Go to each section again, and remove the old QNAP path.
- Refresh each section again, and now movies should no longer be doubled.
- Clean old bundles.
- Empty trash
- Optimize database.
- Go to your device list, and delete your server from there.
- Sign out of plex.tv, and wait 3 min.
- Sign back in.
Sharing with friends might have to be setup again, unsure here, so do report back on that part.
Ohhhh…And QNAP, even if it’s a low powered one, is great for remote windows storage, like for your movies etc 
/T