[Alfdawg]

I just got my 4 channel and subwoofer amp installed. The 4 channel amp is jl audio xd400/4v2 and the sub amp is sundown audio sae 2000d. I have the fark harness and the sub amp is hooked to the pass thru on the jl audio amp. And I also have 2 sundown sa 12s in a ported box tuned to 33hz. My subwoofers isnt as loud as I expected. But I noticed if I turn the bass up on the factory headunit the subwoofers get louder but also does the bass in the speakers and it sound horrible. And also the subs sound good at about 15 but if I go pass that they dont get any louder. So is the factory head unit the problem? Is there a way I can control the subs and speakers separately? Like on an aftermarket radio.