My 'bird is very highly optioned, has the console, A/C, FM stereo from the factory. Mine has the perforation for the center dash speaker, but no speaker under the opening. It does have two factory kick panel speakers plus two rears. Your 'bird probably did not ship with the FM stereo, but may have been either dealer installed (improperly) or added by the owner at a later time. If you have your PHS packet it will show the AM/FM stereo option if the car was built with it.

I'd leave the dash speaker connected, replace the rears, and go with Secret Audio.