If you're happy with what you have and you dont want the hassle of installing a crunch and god-knows-what-type of subwoofer.. I'd say for now stay away from this. And maybe in a few years when you have some funds and more knowledge... you will see that investing in upgrading your internal speakers with clean powering amp will give you more audio bliss than by having just a sub/amp with your stock speakers.

But if you are curious on how it would sound... then by all means brudge that amp into one channel(make sure that the subwoofer is 4 ohms...), use the subwoofer output of your pioneer into the sub amp crossed at about 80-90hz(for starters).

but IMO I say leave well enough alone, because you seem content with what you have now.