Once configured it should work in FCP just fine.
You might want to check the MCU's control setting. The MCU supports 3 different control protocols: Mackie Control, Logic and HUI.
If you have mismatched these settings with what you have defined in FCP then you'll have trouble.
To change your MCU's control setup, first power OFF the MCU, then power back ON whist simultaneously holding down the Ch1 AND Ch2 SELECT buttons ... the display will then prompt you to select the control protocol to use: press the Ch 1. V-Pot to select Mackie Control.
As long as FCP is configured the same should be fine.
best wishes
Neil
http://www.patience.tv