you need to read this http://www.xoutpost.com/articles/x5/s...ctory-amp.html (unless you have an aftermarket head unit)

depending on the stuff he's giving you, you could be better off with 1 10" in a stealthbox. I used to have 2 cheap 15" subs when I was young. Now I have a single 10" that I splurged on and it sounds 10x better. Additionally, if they are a good set of subs & amp, it may be a waste to run off the factory HU. But I'm just hypothesizing.