I have a 07 Honda Civic with a stock built-in dash cd player. Can you hook up aftermarket door speakers and rear 6x9s to it with out an amp?
You can use after-market speakers with the stock deck. I don't think you have 6x9 speakers in the rear, though; most Civics use 6-1/2 speakers on the rear deck. Even then, the stock speaker is very, very shallow; you'll need to use a spacer bracket to fit most after-market speakers in the same space.
Yes, most newer stock stereo's will have enough power to push whatever door speakers or 6x9's you install, it just depends on what you get. I just replaced my door speakers and my 6x9's with some pioneers and I still have a factory stereo but it sounds good! Of course it would be better to install an aftermarket stereo though.
