Ok so the headunit has what 1 pair of preouts?
red and a white RCA output..?
that goes into amp? Get a Y splitter and then that will split your 2 channels output to 4 for input on the amp.
Then you put one pair into the front and the other into the rear inputs on amps.
one way to test your speaker connections are good is just jump them from the amps front channels to rear or whichever ones work.
get 2 of these