I'm not sure where they got the source signal, but it wouldn't surprise me if they used the sub wires coming to the factory sub for the signal into the JL amp. Then they ran new wire to the JL sub from the JL amp.
The system really does sound impressive. I've had the 10" and 12" TW3 as well as W3v2 subs in a few different vehicles, and I have to admit this 13" TW5v2 might sound the best yet. It has very tight, precise bass response, but can still really boom if you want it to. I go back and forth between liking the tight sound of a 10" and the harder hitting boom of a 12", and somehow this 13" seems to accomplish both pretty well.
Another thing I'm impressed with is the sound stage the Mark Levinson signal processing produces. It does a decent job of pushing the sound stage pretty far out in front of you, and the time alignment is really pretty good. I'm sure if there was a true DSP hooked up in the system you could push the sound stage out towards the front of the hood, but for now it at least sounds like it is out a bit past the windshield.
That's a great looking rig. Unfortunately the rear tire carrier is out of stock with no known lead time from ARB, so I'm just going to do two bumper blanks for now and will possibly get the tire carrier later on when it becomes available. Sounds like I need to look up the pinch weld mod, and get out the BFH. We just did a heat gun massage to the new G Wagon to get some additional clearance, so I imagine this will be about the same.
I hope to get the bumpers and side steps to powdercoating this week, and then get everything put on the truck the week after. Fingers crossed everything shows up tomorrow that I'm still waiting on!