Integrating new iMac with TASCAM DM4800 mixing board

Hi, we built a new church and have a new iMac. This is our first experience with an Apple platform and we are very happy with it's performance. We have a digital mixing board that we would like to have linked through our Logic Express 8 software for recording the services. We had our first service last Sunday and I wasn't able to figure out how to get it to record. The DM4800 has the appropriate firewire card installed and it is connected to the computer. When I go into settings on Logic Express, the firewire card comes up - so I know the computer can see it - they just don't appear to be communicating. I'm sure it's something simple - I just tragically assumed we could just plug the board into the computer and we would only have to hit the record button. If someone could just help me set up at least one channel to record - I could then probably duplicate it for the other 15 chanels. Please help.