How can i make my MTX Subs Hit Harder?

What you purchased is an entry level package. To get louder,you could try setting the gain a little higher.( I do not usually recommend this because gain does not equal volume necessarily) If you have already maxed out your gain, and you are not where you want to be, you may need to upgrade to heavier duty equipment. Just be sure your electrical system can handle it. Have fun, and good luck.