Well....you already made your first mistake.
You bought your amp first.

The amp is the "motor" that drives your subs, and buying a motor, befeore you choose yor car, in not wise.

You should have chosen the install first, then the parts that are going to make that install work.

Now you are limited in your choices, because of the amp/impedance relationship that the amp choice incurrs.

You need to find a sub, that works at 4 Ohms, does well with the kind of sound you're looking for, in the space you are willing to sacrifice. How much space?
I'd be looking at a good ported box, with a 12" woofer.
Can you build a ported box?

 

The new Clarion subs sound nice and put out a good kick and they've upgraded the power to 300rms so it would work nice with the amp