It wouldn't be too hard to add. You'd need the socket with the extra terminals. And either add the extra wire to the existing connector or get a connector with 3 wires already (the first option is simpler, really). Then tie it into something like the corner marker wiring.
The DC-DC converter can output up to 265 amps. There's a 300 amp fuse between the DC-DC converter and the underhood junction box. Additionally there's a 200 amp fuse at the battery end of the cable from the junction box to the battery.
If you're producing en masse it'd probably be worthwhile to figure out what Molex terminal they are and just get them from DigiKey for like 1/100th the price.
There's a few designed to work with the A2B digital signal that should work from mObridge, NavTV, PAC, and Axxess. No one has used them and reported back, to my knowledge.
The Kicker Key 200.4 and PAC B&O wire harness adapter is nearly plug and play if you're fine with only bi-amping the front...
Technically it's a bit of both. The high voltage battery actually starts the engine, but there needs to be sufficient 12V voltage for the electronics to power up and to close the contactor to energize the high voltage system.