Hey !
I'm using a different solution with a Synology NAS :
- The Calibre library is in my computer
- I use Synology Drive to sync the library's folder to the NAS (one-way synchronization PC > NAS).
- Calibre use the NAS folder.
So there is 2 copy of the library, the second one is always in sync with the latest change on the main one. It works and avoids all the hassle of network sharing. Maybe it can be done with a RSYNC sync ?
Anyway,
I also share a tutorial (in french) to install COPS manually on a Synology NAS.