it is worth mentioning that if you press the transport buttons and it works but everything is greyed out then you will need to reboot the ipad (with Sonar still running and the meters, track names, transport etc. should all work. I only found out by running around trying to solve the same problem. I think the Mackie control setting may need to be set to singal leds only (not signals + meters)

try this:

Exit  Sonar

Go to C:Users\<username>\AppData\Roaming\Cakewalk\Sonar X2 Producer folder with Windows Explorer and delete (or rename if you're the cautious type) ctrlsurface.dat and ttseq.ini.

restart and go through the setup again...

Hello and thanks a lot for all your input. 
Will try this out tonight, and hopefully I got it running:)

I have an update to my efforts. I managed to get AC-7 working with X2a, but the transport controls, and mute buttons did not work. Only the faders and jog.

do you get the track names and do the controls light up (like select?)

if not leave everything running (rtpmidi, sonar) and then reboot the ipad and restart AC7

Yeah, track names updated, but select, solo, etc don't respond. Tried rebooting the device, but to no avail. Works fine in X1, though.

Did you try Mystic38's tip in post # 12?

Can make a big difference...

I found this useful also. having read this I realised that the select button isn't exactly what you would think. As The XT is based on the physical hardware, the functions in theory should match.

http://www.solid-state-logic.com/downloads/Matrix/profiles/Sonar/Matrix_Sonar_profile.pdf