What's this knob do?

I have a Hifonics ZX6000 amplifier and there's a know that is labeled "level" and goes from 6V to .2V . The owners manual dont explain what it does. Anyone have an explination.
Also i am running 2 amps but i only have 1 remote turn on wire to power up the amps when i start the car. Do i just split off that line (1 wire to 2 wires) to turn both amps on or is there another way?

That knob is an input sensitivity level adjustment potentiometer. In english, it's your gain adjustment. You need to match that with the output voltage on your deck pre-outs for best quality sound. As far as the remote turn-on, yes...just split the wire. The one output is strong enough to turn on two amps no problem.