What you would want to do in this case is go from your headunit out of the subwoofer RCA (if you don't have that use rear) and into one amplifier and then go from that amplifiers output to the other amplifier input.
This way they are daisy chanined so to speak. Hopefully your amplifiers are the same and they have a data link thing that uses a cord similiar to a phone cord. Connect this to both amps as well. Then set the first amplifier to "master" and set the other as "slave".
it depends on the amp, like my RE12.1 has a master/slave option on it so when your running 2 amps you just run a single rca line from the master amp to the slave amp and it works, but im not sure what amps have this option.