Okay, I had this problem with my '94. I was going to put in after market speakers because my passenger door speaker (lower 6x8) was crackling, but the 6x8's run off an amp that has a cros over in them. So if you want after market you need speakers that are only woofers (one way), if you look all the after market speakers are 2 way or 3 way (have even seen some 4 way). So you will have to buy component speakers (woofers and tweeters) and they run about $200 for a set and if you want to do all (front and rear) you will need 2 sets. So I bought a ford replacement and it was $39.13 total. To get the door panel off, remove door locks (plastic pieces that go up when unlocking) they just screw off, take cover off upper speaker just snaps off. then pull the plastic piece with the switches on it, you'll have to pull the top out a little then lift. then take the 2 screws that hold switch plate on off. There is one retainer at the front bottom of door, you'll need a puller, or be carefull and you can use a screw driver. Then lift up and out at the top, becare ful of the handle and panel comes off. For more info on Mach system go to
www.flemworld.com and click on Mach 460.