the biggest alternator that i have seen for the X was at 150A, and the biggest single fuse for the battery is rated at 200A (there are other fuses, like 80A and 50A).

12 V * 150A = 1800 W... so, the car's electrical system is about 1800- 2400 Watts... if you add another 1000W...

regardless of the wires that you will put to the battery and/or alternator, you need to keep in mind the capacity of the battery and the alternator - they can't produce consistently more than what they are rated for... have you considered a separate battery?