Hi farmac,
What protocol have you selected? I found that my Mackie MCU worked with HUI but works better with Mackie protocol so maybe this is worth a try....
See this thread for some discussion on the Mackie MCU - maybe some of the tips will help - the A&H is a fairly new unit so you may be one of the first to try this....
http://forum.cockos.com/showthread.php?t=50609