Thanks!
Light is a Princeton Tec Switch MPLS (ARC Rail adapter sold separately)
http://princetontec.com/switch-mpls
So kicking this around, there is a wire that connects the two earcups that is encased by the leather headband (I wish I'd taken pics of the transformation). You have to cut the leather off to get to the wire in order to mount the headphones to the Arc rail. Then you can pull the earcups off the wires holiding them in place and transfer them to the ARC rail adapter.
If you do have to cut, cut the actual threads in the stitches on the headband and leave the leather intact. Then you can either see it back together later, or maybe see some Velcro in it so it is a removable feature.
As mentioned before, in the OpsCore manual that came with your helmet, it might have a diagram showing how to install the headset with the headband still attached. I found that to be really uncomfortable but your experience may vary.
Note with the light: I had to set my headphones pretty far back on the rail in order to securely fit the light on. I also have it mounted backwards on the adapter so the tab is accessible from the front. Play around and problem solve till you get a solution that works for you. Ain't anyone else wearing that helmet