fried my old amp. want to prevent it from happening again

ive got a pretty basic setup. two 4" in the front two "6x9"s in the back and a 6" sub.

i hooked up my new head unit last night and plugged the rca out puts into my small two channel amp just planning to hook up the '6x9"s i then hooked up the battery connection, the ground, and the last wire the REM. on the original system"sun rotted 3.5s and 6x9s" i think it had the power anttena outlet from the head connected to the REM. this time when I reconected the wires i atached the rem wire to the amp output wire. after a couple min unattended my amp started smokin. had to un plug and disconnect.
did i do something wrong?

i now have a four channel planning to connect the sub and the 6x9's how should i do this?