Now that I had a pair of Kicker C10’s under my rear seats, I needed to add some power.  Looking initially for something small and simple, I browsed the Crutchfield catalog and chose a JL Audio XD300/1v2 amplifier rated at 300wx1 @2-ohms. I liked the XD Series specifically because of its small dimensions due to being a Class-D amplifier… and I didn’t want to mount the amp behind the rear seats (well, there’s no real room there anyways), so I had to pick something that fit under the driver’s seat.

Knowing the audio signal would be limited by the factory head unit, I also installed an Audio Control Epicenter Bass Processor underneath the passenger seat to get some low frequencies back. I used a PAC Line Output Converter to connect the stock Nissan head unit to the Epicenter’s inputs. With the two Kickers, I had more bass like I wanted. However at the same time, it just showed me how weak the factory main speakers were. Eventually I knew I’d upgrade the audio some more, but for the time being this was fine.

Center cluster and center console out, seats unbolted and tilted backward.
Checking lengths and running RCA cables.
Installed the line output converter under the center console.
JL Audio XD300/1v2 amp under the driver’s seat, all wired up.
Audio Control Epicenter, under the passenger’s seat next to OEM Bluetooth module.
Pair of Kicker C10 10” subwoofers. Not the greatest, but good enough for now.
Dual-10” enclosure, down-firing, fit pretty nice under the rear seats.
I like how the subwoofer box lines up with the edge of the floor mat and doesn’t creep into foot space.

UPDATE 02.07.15: Amplifier replaced with an Alpine PDX-V9.
UPDATE 02.07.15: LineLevel Converter removed. 
UPDATE 09.30.16:
 Bass Processor replaced with JL Audio TWK-88 Digital Signal Processor.