This isn't exactly true. While it might work like that, you're changing the output impedance from your stereo by wiring up more than one speaker per channel. Not something I'd really recommend unless you're aware of the consequences. Raise the impedance and you're going to lose volume due to the higher resistance, lower the impedance and you run the risk of frying something. Also like others have mentioned, if you do go this route you're definitely going to want to replace those speakers. I can absolutely guarantee you they're junk. On top of that I'd recommend a separate amp to give you those extra channels, and that would require either an aftermarket head unit with RCA pre-outs or an interface to provide you with some from your factory radio. Lots of money and work for minimal gains IMHO. (Also this is just me but I think that headliner is a little ugly, different strokes though.)