Merlin magix VOIP

We currently have a Merlin Magix PBX and I want to provide soft phone VOIP access for our remote employees. Can some one please tell me (from a hardware stand point) if all I need to do is connect an FXO card to the existing lines coming from the Magix PBX (ones that go to the wall phone jacks) and then I can configure Astrisk to make the extensions associated with those ports available via VOIP?

Any one has a suggestion as to which Digium cards to use? We only need about 4-6 extensions to be available via VOIP.

All hints/suggestions would be greatly appreciated.