How do i Match my amp's gain to my head unit voltage. I have a Alpine 9855 H/U and it has 3 4v preouts i have 2 alpine amps as well a, V12 Digital Mono Amplifier MRD-M605 for my subs which are 2 alpine 12 E-Type and a, 4 3/2 Channel V-Power Series Amplifier MRP-F240 for my inside speaker...