1998 Grand Prix OEM Stereo Layout - FYI

In every book or reference guide for the 1998 grand prix 2-dr GT the stereo configurations list that there are only 4 speakers.(x2 5 1/4"in the lower door panels and the 6 x 9" speakers in the rear deck. Even if it asks if you have the premium sound w/ 8 speakers it only lists the 4 of them. Up front w/ the 5 1/4" are a pair of 3/4"tweeters higher on the door and a pair of 4" speakers besides the 6 x 9" in the rear deck.It also does not say anything about a factory amplifier, which it does have behind the glovebox.With only 4 channels coming from the head unit the door speakers(5 1/4"&3/4")are wired together w/ inline filters, and the rear 4" are run off of the head unit's rear channel power. But the 6 x 9" are the only ones to be powered by the oem amp. The oem amp already crosses over the signal so the 6 x 9" have all bass frequencies, everything else gets full range.It took me TONS of homework/research to figure all this out on my own. Not even the dealership could give me correct answers.With this complex(for oem)layout replacing just a head unit or just adding subs can be quite tricky. This is just a little info for anyone else that has the oem set-up that's not listed anywhere.