Integrating Appointments+ with WebDAV calendars

Hi, I brought Appointments+ to work and I like it very much. Now I just got the thing that I would like it much rather to work with another calendar than then Google Calendar. I want to use it with the Daylite Calendar. Daylite https://www.marketcircle.com/daylite/ is a Mac CRM Software. It has a own shared calendar (NOT iCal), but a own calendar working also with WebDAV. So if I am using this WebDAV Adress it should somehow be possible to sync this with Appointments+ ? I guess not the normal way - but with a programmer doing it? What would a programmer must to in order to make this work?

Looking forward to your answer.

Arne