From bass to full range?

My car has 4 speakers on the rear deck. Two 6x9's and two 5.25's. The 6x9's are only sent bass and low frequencies, but i just got 2 alpines and i want to send full range frequencies to them. What will i have to do to send them full range?

Thanks in advance, :D
-M0ng00se

K, for starters, the model number of speakers you have, might help (all of them). The configuration they are hooked in, any crossovers availible, placement of the alpines ? I only mention this, because, typically, 6x9's are coax, and dont usually get fed just lower frequencies, (less being used for rear fill, and in that case, they are usually not coax).

In any case, kind of difficult to give accurate info. Most speakers will run in full range by default, unless a cross over is in the picture, whethere from the amp, deck, passive, or active. See if you can give a few details as to the configuration of everything. What is pushing everthing and how.

I really dont know much about whats goin on, because its a completely stock setup. All i know is that the 6x9's only receive bass and i would like to be able to send them full range.... :S

My car is a 98 grand prix GT coupe, if that helps anyone.

Sorry i couldnt be more specific, but im just wondering if these speakers will even work at all in my car.