my bro has rear speakers hooked up to a pioneer head unit in his echo, ultimately i'd say you can run rear speakers off the factory head unit but i would check its output first otherwise you may need an amp, my brother was told that the 240watts 6x9 were at the limit of the 4x50w amp of the headunit. It sounds good but bit of work involved in cutting the hatch cover. The sound is good despite it bouncing staright off the rear window. He runds pioneer headunit with Mp3 6x9 240 watts three way speakers in the rear and some better pioneer 4 inch front speakers to relpace the shitty factory ones.