Ok so long story short, I wanted more boom so I installed a Kicker CXA400.1 and a JL Audio 10TW3-D4 running at 2 Ohms getting about 300-350 watts. All of this sounds good on paper but the results are leaving something to be desired based on other installations I have done in other cars of mine with similar or lesser setups even.

The problem I believe is the Fender amplifier and how it's playing a role in getting my audio inputs for the amp. You see, I put a line out converter on the amplified subwoofer outputs from the fender amp which again sounds great on paper because I should get plenty of voltage on my RCA cables. But what my problem is is that higher bass lines like happen in rock music are very quiet and the sub hardly moves if at all and it mostly plays bass through the speakers whereas my rap music plays heavy through the sub because the bass lines are at a lower frequency, this is my observation at least.

So what I think is happening is that the Fender amp assigns each set of speakers with a frequency spectrum that matches the purpose of that speaker and it filters out everything else so for example. The subwoofer may only play 50 hertz and below, the bass speakers play 51 to 120 hertz, the mid speakers play 121 to 500 hertz and so on. Hopefully someone can confirm or deny this is true. If this is true then that's why my sub is only playing half the frequency range it should be, it's only getting supplied with inputs of 50 hertz and below for example and is being prefiltered without the opportunity to see anything higher.

So if that's true, what would my solution be? Since it's a monoblock amp could I simply take one channel of the line out converter and hook it up to the bass speaker wires so I pick up on those higher frequencies as well and then let the low pass filter of my amp take care of filtering out stuff that is too high?

Thanks for any help guys!