sure these will be fine - if you happen to have extra lights, dvd, etc i would opt for a capacitor with a digital display to make sure you have proper voltage - if not you can use 8 gauge wire but i would reccomend 4 gauge to be safe and in case you want to upgrade later
are you installing these yourself>?
remember - run the rca's opposite of the power cable and remote turn on - most people will keep the rca's on the other side of the exhaust which is run on the passenger side - this will keep the intererence down and any excessive noise from the audio signal
make sure your rca's are well insulated - not just a/v cables those these will work but you will see car audio rca's are much thicker
keep the ground as short as possible usually no more than 16 inches if possible
good luck - and make sure all your connections are solid and that your subs are tied down somehow in case you are in a wreck, joyridin' etc
installing speakers and subs in an xj are about as easy as it gets - simple plastic trim and plenty of room for cables etc - it should be easy for a newbie to make a clean install
i am done