This would be very area dependent, as the firmware the provider is using will dictate if the feature is active or not.

If it is active, that plug is a stereo (3 wire) plug. You would need to unplug the box, plug in a stereo cable with the ends stripped, plug box back in and turn it on, then use your multi-meter to find with connection has the voltage for the IR receiver on it. Then chassis ground. And of course the last one would then be IR in.
Still won't know if the IR signal it wants to see is with carrier or stripped until you experiment.


The other way is to wait and see if someone here has already done all this and can give you the answers to the above.