Now that I see your Prelude is exactly the same style as mine, here's the deal on your speakers. The front door speakers are VERY shallow. To replace them with a bigger speaker magnet you need to remove the entire door pannel and cut and shave the surrounding plastic linning behind the speaker. DO NOT attempt to cut it out while the door pannel is on the door.... there are wires and plastic linning back there! You have one inch tweeters by the door locks, 6.5" door kick pannel, and 6"x9" in the back deck. Now, I think you better double check the installation of the previous owner, since the front speakers ran off the factory head unit amp, and the rears ran off an external amplifier in the back deck. Unless they bypassed it, the factory head operated the rear amp, so if they replaced the head, I don't know how they operated the rear speakers, unless their intent was to just use the sub and leave the rears dead. Now, if you are going to run new speakers off the aftermarket head, you will need to bypass the "Accoustic Feedback System". This post is starting to run on, so post with more explicit questions and I can help you out.