Speakers for 2002 Boxter S

[genevax]

Hi, I am new to the forum, and happy to make my first post. I hope it is not inappropriate to make the new thread for this topic. My wife just got a 2002 S with the upgraded stereo. It seems to have speakers in the doors with low-pass filters (I say this because only low frequency comes out of them). The dash has mid-range and high, but it would be nice to have sound come from the rear. We drove a car with the Bose system in it with the rear speakers and sub, and it was great, but the cost was quite high. Does anybody know if there are small, but good quality speakers that will fit in the little holes of the organizer that is located behind the seats? Also, are there enough outputs on the factory radio to drive more speakers, or do I need to put in an amp?

Thanks,
Tim