Clipping is when you square off a sine wave, which is sending your subs dirty power. The only two ways to tell if you're clipping is an o scope or dd-1. Just because a woofer is rated at a certain rms rating, doesn't mean you have to have that amount of power.
From what ive heard, the hfi line is over rated. The aq1200d does 870rms at 2 ohms. I don't know what your budget is, but the aq is around $260.
Edit: wire the aq at 2 ohms, and adjust gain accordingly.
Some will say break in is needed, and some will say it isn't. When I put my sa-12s in my car, I turned it up to my listening volume and let em have it.
Just hooked up my sa-12s, and I love them. They're loud, and clean. Loudest 12s I have heard so far. Big thanks to Jacob and everyone at sundown for making a solid product.