You need a GOOD amp (or you should check your current one a bit better)...
You should level your radio at 0 bass and 0 trebble etc. so that you always can adjust a LITTLE from your HU.
Your current amp has the SUB on it if i'm reading you correct. Every single amp has one of the following options:
- Gain level (might be indicated with ohm numbers 1 - 4 or 2 - 4)
- Frequency (the lower you set it the deeper and heavier the bass will be)
- Bass port (all my pg's have it, kinda the same as frequency)
- Hertz (0 - 150 or something, the more hertz you set the heavier the bass)
If you have one of the options above on your amp (pretty sure u atleast have two) then use those to tune your bass couz these will only effect devices connected on the amp itself and not speakers connected to your HU).
If you really dont have any of the options above then (... it must be one hell of a lousy amp) go to the store and buy a remote bass controll device. I bought one two days ago from Caliber for 20 bucks and it works REAL great. The device has a hertz and gain controll wheel and is connected on your RCA cable so that it only will effect your subs and not your HU speakers..
Humanity my mirror,
Madness what I see