Do i need an amp??

Ok, this is probly a hardcore stereo noob question, but do i need an amp to run a subwoofer? Im doing a custom install in my camaro, and im looking at the wiring diagram from my headunit, which has sub out RCA cables, and in the diagram, it seems to show it hooked directly to a subwoofer in a box, with no amp between the two. I was under the impression that a headunit couldnt power a sub, and that these were pre-amp outputs, am i mistaken?

Also I am running an 8 speaker system off of a 4 channel amp rated at 40W RMS, wired at 2ohms instead of 4ohms, if it is possible to run the sub off the headunit, would there be any point? in other words, would i hear the sub over the other speakers?

and last question i promise, If i have to run a second amp for the sub, do i split the amp remote wire from the head unit and run it to both amps? or will the sub's amp not need that input? and can i run both amps off the same power wire or will i need to run a second power wire from the battery back along side the first one?

Thanks and please, be gentle, im new to the whole aftermarket stereo thing, even though automotive electronics and wiring is what i worked in at the dealership.

oh and i dont know if this is relevant or at all usefull, but the power ratings of the sub are...

32-120W RMS
400W Max
10" cone

and the output on the head unit is 4V, i dont know the wattage though.

nevermind, got my answer, time to go amp shopping.

read first jeez

Hey 89, just make sure you don't get a chepo crap amp for that awsome car. :)

super noob question of the year right here...

what drivers are you useing? JW...and you are planing on building your own enclosure correct? prefabs suck...