The only thing I can say for now is that my A-Pro 800 controls X2a (Essential) perfectly on Win 7 32 bit.
You don't seem to be doing anything wrong, but let me ask these just in case:
When you launch Sonar, does the Act button on the A-Pro light up and the display say "Receiving"?
Which preset do you use in the A-Pro control surface plugin? Does "Tracks/FX/Synths/Utility 2" work?