I just got some infinity 6.5 component with cross over. Could I directly hook it up to the current setup with out using crossover will it work with out. If I decide to use crossover how would I wire the crossover since the wires are split from the factory harness would I connect both negs to the - side and both + coming out of the main to the crossover

 

Use the cross over..
I'm assuming this is a passive set up

On the Crossover:
1. Input: Speaker wire from amp +,- to the cross over
2. Output: Speaker wire to woofer +,- from the cross over
3. Output: Speaker wire to Component +,- from cross over

Edit: you will also need an amp matching the RMS ratings on your speakers I wouldn't advise coming from one you have pushing subwoofer/s