Apple Logic Pro /LogicExpress Discussion

Using Logic Express 7.2 on a G4 - can get audio through  - but can't  
get midi to play - after loading a midi-file The file plays through  
Quick time player - but I can;t get a sound out - using ST Audio  
sound card with a ADC/DAC 2000  outboard unit - Logic express has  
recognised the St Audio drivers - where do I go from here?? Thanks