As a "Hardcore" audiophile, you would probably already know that the most important thing is staging and imaging. So you would already know that putting speakers in your back door would offer nothing to your imaging. The only thing you will accomplish is making your car louder, which has nothing to do with being an audiophile.
The more speakers is not always the better, a high end component,(two way or three, and I said component) in the front door is the first step.
Hardcore audiophiles would then seek a very good amp, and no Audiobahn is not a choice.
McIntosh, Zapco, Arc, old school Xtant,PPI And Butler are all great choices. Oh yea even an old Soundstream class A
Round your amp choice off in a two channell or a four (if you prefer rear fill) and get to fiberglassing, cuz everybody knows hondas have the worst staging issue on the planet.
And now go get yourself a good sub amp and an sq woofer to round out your audiophile system.
Hey if you get carried away and want more speakers go get yourself a dvd player center channell and a 5.1 processor..
But if you are a "novice" to this hobby, go ahead and cut your back doors and add some speakers