The input level is determined by the head unit. What kind of head unit do you have? To set the gain, start with the gain all the way down, turn the volume to the point where you hear distortion, then back off until it stops. This is your maximum signal to noise ratio. Then turn the input sensitivity until you hear distortion, then back off until it quits. Do this with your equalizer set where you will have it. If you set the gain before and turn up the EQ later, you'll need to readjust the gain. LPF is your preference, and it also depends on where your other speakers leave off (for example, if you set a HPF for a component system at 100 hz, the subs LPF should be at 100 or maybe a little higher.) Bass boost is not necessary, but if you want to use it, adjust it to your liking. I don't usually set bass boost as it can damage speakers at high volume and clip quicker.