Here is some powerbass stuff, don't know if you have herd their subs but I personally love their products, here is a link to a great sub, they don't take up a lot of space and sound great in a ported box.PowerBass Xtreme XL-84 Subwoofer | PowerBass USAI am looking for an EASY solution to add more bass to the Koup without taking up a lot of space and costing a lot of money. This seems like the best plug-and-play powered subwoofer I could find and I am able to get it for approx $430. I am also leasing the Koup so take that into account.
I also considered the Infinity Basslink and the JL Audio PowerWedge but this seems to be better.
Here it is on Crutchfield's site with 2 positive reviews at the bottom:
Rockford Fosgate Punch Overload PS300-12 300-watt 12" powered subwoofer at Crutchfield Signature
Here is the only review I could find for it but it is very positive:
PASMAG | PERFORMANCE AUTO AND SOUND - Rockford Punch Overload PS300-12
Basically, I'm looking for any opinions or comments regarding this product.
Then a amp to do the job (if you get 2 subs), would be this PowerBass Autosound ASA 600.1Dx D Class Amplifier | PowerBass USA
Then if you just want a single sub, I would get this PowerBass Xtreme XAX 500D 1-Channel Mono Block Class D Mini Amplifier | PowerBass USA
The difference between the amps is that the ASA models are the good range, and the XTA amps are their top of the line amps (Xtreme). The reason I mentioned the 2 amps is because if you do decide to just go with 1 sub you would not want a full 600 wats going to it, 500 wats would be better just to make sure you don't blow it.
I don't know how much it will cost you because all dealers are different. Just an idea for ya, I hope I helped somehow. If you have anymore questions or help just pm me if you want and ill TRY to answer them lol.