HELP! my setreo is horrible
 

i am trying to run two amps to one subwoffer. my original aps is 600w max and i came across a 100w so i thought i would try and add it in to give the sub a little more punch. i have no idea how to add it into the existing work. i have the power ground and remote already set up i just dont know how the rca's would work and how to hook up the speaker wires to whats already there. any help would be greatly appreciated. thanks