Adding more speakers?

[Life2]

I have a gen 3.5 without premium sound and so far I've upgraded the headunit and all four speakers. I was wondering what I would have to do to go about adding more speakers? Ideally I'm looking to put a speaker in each of the back door panels (I believe there should be enough space within the door frame to support this). Im just wondering how I would have to wire things up. My friend says I can just splice from my rear speakers and run these door panel speakers parallel to them without directly wiring them to the headunit. Just wondering if this would work or just end up doing nothing.

[iovaykind]

First, I'd get an external amplifier connected to your head unit. If these are 3 or 4 way you can hood up a subwoofer to it, as well as two more speakers. So power the extra speakers with the external amp. You really don't want to run anything parallel, unless the speakers are 8ohms and your head unit runs at 4ohms, in which case running two in parallel will bring the resistance down to 4ohm.

[Life2]

Thank you! that was an excellent response!