ive checked ours a little while back the wife has the bass box option and the speakers in hers are identical to mine, the only thing she has extra other than the bass box in the boot is tweeters in the back - ours are both multiwagons.
i run my speakers off a kicker amp, the only reason why i done this was i needed dual zone so the kids could watch a movie in the back whilst i listened to the radio / mp3s in the front, the kicker done the job fine, i just got a generic iso block to connect the speakers to the amp then iso to the back of my pioneer hu.
tbh the speakers fiat supplyed in the cars are not the best, but they are pretty good, they do take a bit of thrashing before they start to distort, i could probo do with bigger speakers in the car but what aint broke as the old addage goes, and my infinity bass box with built in amp takes up the slack where the speakers lack. plus as you get a bit older you dont need the music as loud funny enough lol
roy