Hi there and welcome to the forums

If the Calais cluster is brand new, then only fit the cluster at the dealership.
(After 10Kms from memory, the Kms on the cluster cannot be re-programmed by Tech2)
Holden added this limit to Tech 2 as some dealers were whoring out new cars to managers, sales reps, and the like, and then resetting the Kms back to near 0.
Your best bet is to remove the cluster surround trim, and make it as easy as possible for the dealer to swap your cluster and program the new one.
If the Calais cluster is used, then the dealer wont be able to program the Kays on it, so it wouldnt matter if you fitted the cluster and drove to the dealership, or supermarket, pub, etc)...
Also to answer your rear Aux question,

X3 Connector Pin 9 is the RSE Right Channel Input (Rear DVD Player)
X3 Connector Pin 3 is the RSE Left Channel Input (Rear DVD Player)
X3 Connector Pin 4 is the Ground for the above inputs.
The X3 Connector is the bottom LHS Connector (With the blue numbers)
Oh, and to get these inputs to work you will need to enable the RSE Option on your IQ Unit (Via Tech2)
This will also allow you to use the Video Input for RSE
I hope this helps