Can you wire an amp and 6x9s into the original headunit

Hi all
I know it probably been asked before but does anyone have a how to guide or know how to wire a amp into the original seat headunit also what equipment do I need as have all the remote wires speaker wires and power wires ready is there anything else I need?

Thank you where abouts would you but one from and what or where would you attach the wires too cheers callum