Photos of the trunk of a CRX please!! I have no clue what it looks like. I recently did a pair of ID8v3's in a Civic Si. The box was only 0.7 cubic feet, and it sounded GREAT. You could do one 8 ported as well. This pair was sealed. Add 300W and it sounded great.

Personally, if you want to go loud, you will need a few things. First, I'd recommend more power to your speakers. Also, you will need a crossover to take the bass out of your small speakers and redirect them to the sub.

If it was me, I'd get a 50x4 amp. Run the front 6.5"s from it, and then use the other two channels to run a single sub or a pair of them. Then run the rear speakers off of the headunit.

This way, when you turn up your music, your highs will be able to stay loud and clean, and you will also have some pretty good bass.

Like you said, not winning any competitions, but some nice balanced sound. I'm sure there's places to hide stuff, but I'm not too familar with the car.