
I have a 60cs and I'm guessing the process will be the same. From the skyplot screen (the one where you see which satellites are locked on) press 'MENU' twice. Select 'INTERFACE' from the icons there, highlight it and press 'ENTER'. Then select the 'Serial Data Format' field and press 'ENTER' again. Next select 'NMEA In/NMEA Out' from the drop down list. Press 'ENTER' to select it then quit back out of the menu. That should do it but if not then check all your connections.
FYI EGNOS is on now (mostly!), so when you see small letter Ds on the bars in the skyplot screen you will be getting better accuracy. than on a non EGNOS/WAAS compatible reciever.