Last year I bought a new car and upgraded my car stereo to a high end
Alpine CD Player (CDA-9835), 6 Infinity Kappa speakers (4 speakers and
2 tweaters) and my old McIntosh MC420 amp (4 x 50 watts). The amplifier
is amazing, but ever since I bought the system, it has never sounded as
good as I thought it should. I never did anything about it until today,
when I took off the frontplate on the amplifier and moved the levels
from 2V to .3V. Wow! What a difference it made. It was like listening
to a whole new system! Besides kicking up the power considerably, the
bass is finally where I feel it should be. I think the reason the
installer brought down the levels was because of a hiss that I heard
when I first bought the entire sytem. It is now gone. Unbelievable.
It's amazing what a little tinking can do. My question concerns the
other knobs on the amplifer. I don't want to touch anything else as I
don't really know what it all means. Here are the current settings:

First button says 150 Hz. There are three options (Flat, -3 and -6dB).
It is set for -3.
Second button says Channels. Three options (2, 3, 4) It is set to 4.
Third button says Hipass Filter. Three options. (120, 80, OUT). It is
set to 80.
Fourth button says Subwoofer. Three options. (120, 80, EXT). It is set
to 120.
The remaining buttons are the levels I was tinkering with. The option
are 1, 2V and .3V.

I do not have a subwoofer in the car and it is using the standard
battery. Can someone explain to me what these other settings are and
what they will do to the sound/power of this system? What else can I
adjust that will make the sound come alive even more without damaging
anything? Thank you all in advance.

Steven