Audio Systems: Bose system in 02 infiniti i35, bose speakers, bass amps

Question
Im trying to replace the headunit if my 02 infiniti i35 but keep my navigation.
I have 2 12" 400 watt subs in my trunk powered by a 400 watt 2 channel amp,
as well as the factory bose sub. It just puts too much bass in the car that i
cant hear the speakers. The bass isnt good quality either. I wanted to replace
the headunit but they dont make a dash kit for my car, unless i took out my
navigation which i dont want to do. I also dont want to tear out my bose
speakers incase i sell the car. What do you reccomend i do to make the bass
sound better and get better quality out of my bose sound system

Answer
First, you need to balance the bass levels.  Turn the bass level way down and bring it back up slowly while listening to a recording with lots of bass.  Tuning the system this way will improve the overall sound quality.  (If the sub amps do not have input level controls you can add them ahead of the amp inputs.)

If you tapped off the Bose output to feed the bass amps that is the problem; Bose uses non-standard levels and you must attenuate an extra 20db or so to bring the level down to where other systems are operating at.

Getting the signal level down in level will greatly effect the overall system performance.  If the input of the sub amps were being overloaded, for example, which they probably were, that could compound the bass sound quality due to the high distortion when overloading occurs.   This may solve your entire system problems.

Regarding the replacement of the Bose head unit -  I cannot advise you to do it unless you gut out the entire system and start afresh.  The reason, again, is because Bose is a non-conformist in design and does not match with other equipment manufacturers.  If your unit has the speaker mounted amps you will have to gut out the speakers and replace them as well.  Bose uses very low impedance speakers in most systems and they do not work with conventional speaker designs.  You may want to contact crutchfield technologists who know the cars and what will work in them better than just about any one on the planet.  Be prepared to give them more details about your car and system as the Bose systems are not all the same and they must know exactly which variation of the system you have in your 02.

Best wishes,
C