You can look here, and try to get sync Calibre folder.
I've been testing this hack for months, and it works. I decided to describe it and share it with you.
You can mount over WiFi your Boox device (Note Air in my case) to work on files on the device or you can also use it for synchronization.
I hope you'll like it. I keep using it all the time.
https://github.com/mmagnus/boox-wifi-mount-sync