Either the Kicker ZX850.4 or the ZX650.4 amp in their car. I want to get an idea of it's efficiency and how it performs. I'm planning to use it to run the door speaker Bost Acou, and maybe a small sub like a10". Not into lots of boom anymore but want crystal clear output. BTW I'm planning on keeping the stock HU. Any input would be greatly appreciated before i purchase.