i have to say that a wire harness you can buy that bypasses the amp is news to me,(not to say thats not true)but i just cut the plugs off and wired them together,like i said you need a schematic.this obviously is done in the trunk.you should already have the harness for the head unit,so thats not an issue,anyway,you can still use the stock amp for the sub with an aftermarket radio,you just need to understand what wires are what,it is true that the other amp is tied in with the sub amp,but if you understand whats what then you caN still make it work,from what i remember the plug for the sub amp on the right side with the red n yellow wire is power n ground,i know fer sure the red wire is hot,anyway that leaves what you got on the left side which is gonna be a)=remote turn on)b=1 channel of speaker wires.the 2 that look the same are gonna be the 1 channell,now what you would have to do is,since your using all your channels on you head unit is make sure you have a head unit that has preamp outputs (rca jacks)run a patch cord to your trunk n put an inline converter that goes from rca jacks to speaker wire input,n hook that to you amp.you can also buy rca cords that have a remote turn on wire in them,n obviously the remote turn on wire on your head unit is the blue wire that might say either antena or remote.