btw- wait till you get the Alpine in the dash to decide on tweeters... you may find its ok for you with the deck replacement...

It will make a huge difference (if you are using the stock deck now) once you install the new 7894.

The tweeters in the dash really dont sound all that bad, with some power going to them... leave them hooked up with the new deck, you'll probably have to fade to the front to even out the sound. If thats still not enough, try to get rid of the front pioneers and upgrade to a decent component set.