I am installing a 2-way active + sub system in a 2007 Civic sedan. Power will be provided by a single 5 channel Kicker ZX700.5 (sub channel is rated at 280 @4ohm / 420 @ 2ohm - under rated per reviews and birth sheets). Head unit is 880PRS.

I certainly have enough power to run a X12, but is this even remotely viable for an SSD in a sealed enclosure? As I would like to stick with 5ch amp, my pother choice is a Polk Audio PA1100.5 which is 1ohm stable and can produce 600 watts (not sure about actual output on this model).

Keep in mind my goals are to have better than stock sound and my musical tasted run from jazz, to classic rock, punk, salsa, electronic, hip hop, etc. I guess I am wondering if the X will be enough? For comparison I was considering the Alpine 1242D (cheap, good reviews), and Dayton Ref 12HF (lower power handling SQ driver, good reviews).

Thanks in advance for your input.

This is just something to think about, there is no problem with underpowering a subwoofer at all. Even with an extra 400 watts it really wont be louder to ear, if you try to get a more powerful amp for the SSD. Either choice will fit your goals.

Is that amplifier 5th channel stable to 2 ohms?

Another choice not to forget is the SSA DCON.

Sounds like your going for a more subtle accurate style system with the sealed enclosure. I would lean more towards the X or DCON.