I think you're on the right track. We haven't tested those Inifinity drivers for fit or performance in that vehicle, so I can't speak to how they'll sound, specs wise they seem to be a decent fit. I'm sure lot's of folks here would like to know how they sound.
That said, I think the bigger question is what type of bass response you feel is missing. If it's midbass (higher bass guitar notes, tom drums, etc.) you think is missing, pursure a different speaker solution. However, if you think it's lower bass frequency (low bass guitar notes, kick drums, hip hop beats, etc.), you really need to consider a subwoofer solution of some kind. It might be both, too.
The right subwoofer (sealed enclosure) will allow you to have more of both, but if you ask a subwoofer to play midbass, you'll move the image rearward, but it might be worth it for you to have a simple solution. Consider our xh108 system. This system can be tuned to play into the midbass range in addition to the sub bass range. Here's a link
http://www.bavariansoundwerks.com/pr...I=509/_cid=196