so i've been toying with the idea of picking up a set of 6x9"s or something, and cutting a hole on the shelf beind the back seats (i have a coupe) and sticking them in. any reason not to do that? and also, how would one go wiring them up? my two ideas are either a) run new wires to the front and just splice them in with the rear speakers so i have two speakers on one output, or b) plug them into my second set of amp outputs. dont know if that one would work though. so give me some feedback...

you could just use another amp to power them...splicing would work but power would lack...why do you want more speakers tho? just waste the money on a good set

personally I think that would be a bad idea. Placing more rear speakers might give ou more loudness, but in terms of sound quality, the rear speakers should be considered for "fill" only. You should hear sound balanced towards the front, so the sound is coming towards you, and the rears allow it to envelope you and balance it, placing more speakrs in the rear, likely will give you more sound from the rear, and when is the last time you went to a concert and turned your back to the stage to listen to te music?

meh, it was just an idea....