Greetings,
The EXT trigger input on the 4472 corresponds to PFI0 on that board. I suggest outputting the ao/StartTrigger to the PFI0 on the PXI-4472. To do this, you can do this using the DAQmx Route signal vi. If necessary, you can route the ao/StartTrigger signal to a PXI_Trig line and then route from the PXI_Trig line ot PFI0.
I tried opening up your code, but it not include all the necessary sub VIs.
Hope this helps,
Anuj D.