To the experts!!!!

What can I possibly to the the below mentioned system to improve the quality sound of the bass...at the moment its running at 2 ohms, the inside of the car shakes like an eathquake, lights dim slightly at hi volume, i have not change the cars alternator (cost too much money!)
the mammoth Hifonics its at 18 db, 3/4 of the max power, subsonic at 0, phase 0



Car: Honda Civic 1992 sedan
System:

Amp1 => Hifonics Brutus BX1500
500 Watts X 1 @ 4 0HM
1000 Watts x 1 @ 2 Ohms
1500 watts x 1 @ 1 Ohms

General Specifications
RMS Power Range : 500-1500 Watts
Number Of Channels: 1
Maximum Power: 1500 Watts
Built In Crossovers: Yes
Channel Separation: No

Amp2 => Rockwood X-plore
800w
400 rms max
4 channels

Subs 12": Pioneer TS-W126C

Watts MAX. Music Power 1000 Watts
Watts Nominal Power Handling 400 Watts
Frequency Response 18 ~ 500Hz
Sensitivity 89dB
Ohm Rating SVC:4, DVC: 2 or 8

Enclosure: Basslammer Ported

Doors and Rear Spkrs: JVC 200 watts

Power Source: regular batt and an extra BMW 740 Batt