i just bought all new infinitys for my 07 m3 sadan. What I want to know is if there is already a crossover in the car that i just need to take out and replace, or if i have to rewire for a crossover. I know it a simple concept but I don't want to just jump in and get something wrong. I think the main reason i'm confused is becuase there is already wiring to front speakers and to the tweeters. Isn't that what a crossover is supposed to do, seperate the audo for high, medium, and low?