Camera Trigger

I fly the Sony NEX7. I currently use this board for FPV and camera trigger.

It works well. However, I also want to be able to trigger the camera via Pixhawk for survey missions.

Can I use the Aux output as described here,

To drive the HDMI to AV board? If so, Would I maybe need a toggle switch between the Receiver and Pixhawk to toggle between the two control methods…

Or, Is my thinking completely wrong…?

Maybe if I re phrase the question. What is the difference between the rcvr out put and the aux output of the Pixhawk?

Can the rcvr out simply pass through the Pixhawk?