I was using a Rockford Fosgate P300-8P which just barely fits under the passenger side rear seat, but it presses into the underside of the seat preventing easy recline and taking up all the storage on that side. Sounded good, but not a fan of the downsides, so I'm trying out something a bit crazy. I'm now using a Kicker CX400 amp hooked up to the factory sub. Why? To bypass the absolutely garbage bass boost done by the factory amp (seriously, whoever programmed the factory amp for the sub needs fired). Only done a little bit of listening so far, but combined with replacing all four 6x9s with Infinity 9620CXs, the bass output overall is decent. Might be worth sticking with to keep the functionality of under-seat storage.
Edit: disregard below, turns out letting the truck just sit... fixed itself.
PAC has just released a revision 2 of the AP4-CH41 which works with unamplified (base) systems. That is irrelevant since I have HK, but it may be causing me an issue... not sure if anyone else has gotten a new unit yet. None of my cameras are working since hooking up the unit. Not sure if it's firmware related (don't see how it would be unless the PAC somehow affects the info going into the headunit), or there's an issue with the wiring harness. So far as I can tell everything else is working. I tried unhooking everything behind the screen and plugging it all back together, as well as a few battery terminal resets and have had no luck... tech support is going to talk to engineering tomorrow. I may hook the stock harness back up to see if it works. Just annoying because I wrapped everything in felt tape to prevent vibrations/rattles, and the more I take the screen our the more afraid I am of breaking clips, etc.