Nearly any 6.5" will fit the doors. With slight mods, a component set will replace both the mid-bass and tweeters in the doors.

As for subs-there are 1 or 2 recent threads about what aftermarket subs will fit and how to do it.

No matter what you do: the "Biggest Bang..." should be first. It does help tons. Just not enough for me! I hated the OEM setup. Went with Infinity 2-ways in the doors and a Pioneer HU.

World of difference!