iCal Bi-Communication

Hi people,
Loving my new Classic. One question. I have a private mail server at my company where I have an ics file for my calender. I can put appointments etc from my webmail application. I see the same changes on my computer via Thunderbird Lighting which syncs with the specific ics file. When I edit something on either my Lighting callendar or webmail callendar it shows up in both. I saw my Classic only syncs subscribed callendars meaning I am not able to edit it. I dont have CalDav support on my mail server (Axigen). Is there a way to do it?
Regards

Demetris