Visit this :
http://www.civinfo.com/forum/158836-post6.html
You will see my amplifier (5-channel) and in some pics below you can spot the crossover of the front speakers(morel) and the Phonocar adapter.
With these adapters you drive the speaker wires of your Head Unit onto them, and rca cables come out going to the amplifier. The correct way to do that is to have short cables coming directly from the head unit to the adapters. Then the rca cables will go to the amp and then speakers cables from the amp to the speakers.