Im trying to set my system for optimum performance but I dont understand the whole Hz and frequency thing. as well as the gain. Here are a bit more details that might help out.

Amp: Punch P8002 - 800 watt 2-channel amplifier
200x2 @ 4 ohms, 400x2 @ 2 ohms, 800x1 @ 4 ohms, 12dB/oct Butterworth HP/AP/LP crossover variable 0-400Hz, RCA inputs, RCA pass thrus, cast aluminum heatsink, military spec PCB, and remote Punch Bass EQ with 0-18dB @ 45Hz. H 2.4" x W 11" x L 17.7"

Sub: JL Audio W3 500watt in Stealth Box enclosure

Radio: Pioneer AVH-P4200DVD

 

Is the amp for highs mids or lows?

I have never heard of MHz on a car amp. Normally it is Hz or kHz.Basically you want to make it so the speakers dont get low notes, and the subs dont get high notes. This allows them to play in their optimum range. Then turn the sound up as high as you are ever going to put it on the head unit, and start turning the gain up from 0. Turn it until the speakers are clipping or sound distorted, and then turn it back a little bit so it sounds good.

 

You might want to experiment with it, but it sounds like this amp is driving your subwoofer. Some amps have both high pass and low pass crossovers. You want to set the low pass crossover. I find most people setting low pass crossovers in the 60-150 hz range. Some it has to do with how efficiently your door speakers handle lower frequencies, and the rest is personal preference. You may be able to set your high pass though the head unit. You'd want to set it either at the low pass setting or 10 to 20 db higher. The slopes take care of the frequencies between the low and high settings.

I have my low pass set at 100 hz at a 12 db slope and high pass at 120 hz at a 24 db slope. If your amp is on the back wall, you might want to put cable ties on the locking mechanism for the seat back so you can access the sub while you experiment. Leaving the seat off just allows a lot more noise through the rear vents, making it harder to judge because of the road noise. If you have the ability to set your low pass through the head unit, set the amp's low pass to 200 hz and just adjust through the head unit.

 

yes this amp is for my sub. Im currently running my highs (oem speakers) from the radio (Pioneer AVH-P4200). I went ahead and set the low pass filter at about 90 hz. And the gain was turned up until the speakers started to clip and distort. The Amp has a bass booster that can adjust the curve.
Is there a way to adjust the hz for the highs through the radio ?

 

Some head units have that ability. I'm not sure if your unit does, but the specs or the owner's manual should tell you.