Speaker/Crossover Questions

I recently put an Eclipse 8443 with an 8 disc changer into my 99 eb expedition, it made a huge difference in the sound and gives me a lot more versatility for all the different types of music I listen to, so far Im very very happy with this deck.  I planned on replacing all of the speakers with focal (I think they were poly's, the local shop loves them and some friends there really suggested them).  Tonight I was listening and realized how happy I am with the factory speakers (it was the mach system), so the front speakers are crossed over as a hp filter at some high range (dont remember exaclty right now), I want to cross them over with a low pass also that will send off all frequencies that are too high (the signal tends to flatten out on really high volumes with really high frequency sounds.  So I want to cross them over and send the excessively high frequencies to a seperate tweeter.  My questions are...

1. where or will I be able to find a really high frequency low pass filter to roll the signals off with, or would I be better building a passive crossover myself

2. does anyone know of a really high quality just tweeter with no midrange (focal, mb quart, boston) and where might I be able to get a good deal on a set

3. does anyone see any reason not to do this

4. how much of a difference will adding a 2 channel amp to the front make? is it soemthing I should look into right away (I have other things for the system that would be nice to get right now)

Thanks for all the help

1.  You are looking for a notch or bandpass filter.  Since you are not using an amp you will have to use a passive crossover.  Look for a 3-way crossover and use the midrange output for your OEM door speaker and the high output to your tweeter.  Or yes, you could build one yourself.  What's providing your bass?

2.  There are LOTS of high-quality tweeters available.  If you plan to get Focal's later, look at their tweets.

3.  The only thing I question is keeping your factory speakers as they are crap compared to an Eclipse head, but hey, if you like the sound, go for it.

4.  Probably not much difference with the factory speakers.  Indeed it could hurt.  But after you upgrade to those Focal's you're looking at, yes it could help a lot.

5.  What's providing your bass?