you will need to get another amp, theres no way around that, if your head unit has 2 PAIRS of RCA's you'll be ok, but if you only have one PAIR you could either use a splitter from the rca's on the head unit, you may loose a bit of volume because of the signal being split, or if your amp has a line out, you can use that, but being that almost none of the 2ch amps ive seen have a line out, you will have to go the first option