system for 87 buick grandnational

i have a 87 buick grandnational with concert sound system from the factory it has tweeters in the dash 5.25 in the doors and 4x10s in the rear deck .i want to replace this system. i have a directed electronics 6 channel amplifier and a jbl 1200.1 for the subs and 4 10 inch pioneer premier subwoofers. i wanted to know what i would need to make sure that the interior speakers keep up with the subs.the subs are 350 watts rms each in a sealed box

Go with a good set of component speakers up front.  You can put the tweeters in the factory locations.  See if you can use some spacers to fit some 6.5's up front.  If not, go with 5.25's.  Scrap the 4x10's (they are weak by design) and go with some 6x9's or some round speakers.  Buy speakers based on how they sound- go demo several different sets at the stereo shop of your choice and buy what you like.

-------------
My ex once told me I have a perfect face for radio.

I would go a slightly different route than geephearder. I would scrap the rear speakers and the front tweeters completly. I would use a 5 1/4 coax with a directional tweeter or a 5 1/4 compnent in the front doors and then  I would do a set of 6 1/2 inch compnents in Kick pods up front. I would use 4 outta the 6 channels on that DEI amp to run the 6 1/2s, using 2 channels to run each speaker and the use the remaining 2 to run the door speakers. You might end up with a slightly goofy soundstage but anyone who is running 4 tens obviously wants to be heard and wants to be loud. I think this is the best way to do it.

-------------
double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer