This is what Matrox says about the Express card slot on MBPs:
>>>The MXO2 must be connected to the express34 slot to function on a MacBookPro and requires the full bandwidth from the express34 slot to work.
Since the full bandwidth from the express34 slot is exclusively needed for the MXO2, it’s not possible to connect the MXO2 to an eSATA port or allowing a passthrough for eSATA drives. Therefore, there isn’t a workaround possible to connect both the eSATA drives and MXO2 to the express34 slot.
If you must connect the eSATA drives to the express34 slot, then you cannot use the MXO2 at the same time. <<<<<