Looking at the preferences dialog for external controller, it appears that only one device is supported.  There is no obvious way to configure a second controller like the extender or the C4, and neither of those are in the rather short list of controller options.
                                          
                                          Zemlin thx for the feedback.  Like most posts I have read here and elsewhere, It seems that AA2.0 only supports 8 track external controllers.  That is rather disappointing, considering how powerful this software is especially with unlimited tracks.  Hopefully an update is underway to address this as well as other issues: vsti and improved midi support.
                                        
 
                                        I decided to contact Mackie about this situation.  This is the responce:
                                        
                                        Hey Raul,
                                            Thanks for writing!  The MCU and XT are compatible with
                                        Audition, the C4 however is not.  Hope this helps, thanks!
                                        
                                        All the best,
                                        Evan Middlesworth
                                        Tech Support
                                        Mackie/Crate/Ampeg/Tapco/EAW
                                        
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                                        So 2 out of 3 is not too bad.  I kinda figured the C4 would encounter problems but its good to know for certain that the MCU and XT extenders work with AA2.0!