Assuming your power wire is able to handle both amps' current draw...
-Buy a distrobution block (preferably fuses)
-connect it to your power wire near your amps to split your single wire into two, run each new wire to the + terminals on your amps.
-run a ground from your new amp to chassis, just like your sub amp...
-split your remote turn on wire so both amps get the signal.
-run a new set of RCA's from your deck to you new amp (if your deck only has one set of outs, buy Y-splitters for your RCAs to split the signal, you may also be able to run RCA's from one amp to the other if either of them have RCA outputs)
-run your speaker wires to the amp
-tada.
if any of that didnt make sense to you (which I'd bet you are lost).. go to a shop to get it installed, make cost some money, but you dont risk f-ing things up which I get the feeling you would if you did it yourself.