400a isn't that bad for 4000w.. somewhere around 70-75% effieceny. not amazing, but not badwhoever keeps spouting out these numbers is just guessing
it's a PWM regulated power supply driven amplifier, so theoretically, it should make the same power on 11-16v, the only difference would be how many amps it has to draw to do it
and i've heard some ungodly estimates at how many amperes these things draw
somewhere approaching 400A