crossover

Ok, While patiently waiting for your guys response on my previous question\topic I have came up with an idea that I am not sure of at all. I have decided I want to replace my stock speakers in my 99 blazer with something a little more special. This would include the 2 tweeters in the dash the 2 mids in the front doors and the 2 mids in the rear doors. I have been looking for some component speaker sets on Ebay but I have not decided on a specific one. That is not what I am asking about. The question I have is that almost all of the packages I have found come with a crossover to seperate the mids from the highs. Do I even really need to install these if all I will be doing is removing the stock speakers for all 6 locations and replacing them with the new product with factory wiring? I understand what the crossover does and its importance if running them from an amp. But what about using the factory wiring? Would the crossovers have any use at all and if so how would I implement them into the system without an amplifier? I am sure you get what I am talking about but just in case I will delve a little deeper.(Sorry for the paragraphs I tend to write I just like to get it all out at one point instead of carrying the thread on forever).....I take the left tweeter out snip the wire on both terminals make it nice and pretty again and reconnect it to the appropriate terminals on the new tweeter and mount it in place. The same process repeats itself for the remaining 5 speakers. If this would not be benificial to me in anyway regardless of the fact that they are aftermarket speakers let me know ASAP before I get impatient with auctioning(I spend way to much money on ebay lol)

The crossovers that come with your new speakers are designed to work with those speakers.  The crossover in your OEM setup is designed to work with those speakers.  If you are extremely lucky, the new speakers may sound OK, but chances are they will not sound as good as your system sounded before.  It may take the addition of an aftermarket amplifier and use the crossovers supplied with the speakers in order to get an improvement in sound.

What about replacing the OEM crossovers with the new ones. I dont know if that is in any way actually possible but if so do you got any clue as to where I may start digging around in my dash?

If your vehicle has components in the door from the factory, chances are it has a bi-amplified system.  There is a crossover built into the factory amplifier.  A different kind of crossover.

It has been a few days just wondering what your take on the 4x6 thing was.

Correct The tweeters in the dash are mounted in a 4x6 plate that I discovered could unbolt rather easily leaving about 1 3/4" depth.