You should be able to retain the standard tweeters if you dont intend purchasing splits. Just run the factory tweeter in parralel with the fronts and put a capacitor in series with the tweeter to form a high pass filter.
I have a VT II Exec, so there are no factory tweeters, but the mounts are there for them.
I'll just run some tweeters in parrallel to my fronts to help with imaging.
I have 6.5" Pioneers 3 ways in my front doors running off an amp. SOunds alright, but lacks a bit of imaging.
Standard speakers wont hack high powered aftermarket head units.
I seriously need to replace my rear door speakers.
Currently I have a double DIN sony with rear door speakers running off the head unit. 6.5" pioneer 3 ways up front and 12" sub running off a 4 channel amp. Sub woofer box tucks perfectly under the height of the cargo blind too.... Honestly, the box is flush against the rear seat and tucks under the cargo blind by a bees dick. I swear the sub box i have was made to fit the wagon!
CHeers