Kicker makes a 4 channel amp that's more powerful, cheaper and comes with an automatic dsp for fine tuning the sound. It doesn't come with a plug'n'play harness, so you have to do some wiring yourself. If you have any experience doing stereo wiring its pretty easy
Kicker makes a small amp and dsp that'll fit behind the head unit. It comes with a mic for automatic tuning. model #47key200.4. I believe its less expensive than the beat sonic too.