...but don't want to do a complete overhaul or add additional amplifiers, Elemental Designs has a sale something cheap on their OEM replacement drivers. It's an 8" and works very well IB according to their tech I just spoke with. Here's the catch, the shipping is kinda high but if you order enough of them, it's not that bad so get some buddies together and get a few or get multiple for backups/side projects. I'm thinking of ordering a pair or 4 just for the fun of it... so at $5 each, who can pass it up? The shipping will run you $9 if you buy one but will only be .50 more if you get a pair of them. Shipping was only $20 for 4-5 of them so again, split it up or buy backups. It's not a phenomenal sub by any means but it's an upgrade from OEM and will work off the stock amp. I haven't checked the impedance of the stock sub but you can get single 2 or 4 ohm drivers. Enjoy.
http://www.edesignaudio.com/edv2/pro...roducts_id=448