You just plug the speaker wires from your factory system into it. Each pair of channels has their own inputs and level setting knob. On the other side are plugs for RCAs to plug into that go to your amps.
That and 12v/remote/ground and you are good to go.
My LC8 is for sale. PM me for a price if you are interested. It is mint and worked wonders when I needed it.
For more info you can download the owners manual from audiocontrol.com.