I respect the Beckers, I wish I had the one that came in my car, but it's limiting, least one that age.
I'd recomend, in my semi-profesional opinion, the best speakers you can get that drop in and a good amp. It can be wired in so as not to disturb the factory connections, it'll just be work. I don't imagine the OEM headunit is going to push any "good" aftermarket speakers, and contrairy to popular belief, UNDERpowering a speaker will kill it as fast or faster than overpowering it. Not to mention it will soud less than ideal.
Mine are still original, but everything else is not.
Kenwood MPV-619
Sirius satalie radio
Kenwood Music Keg (
www.phatnoise.com)
It's a start.
/edit/ If no amp and your staying with the Becker for sure, look for a lower wattage rated speaker, with a high sinsitivity rateing.
www.crutchfield.com as well.. They are outstanding in every way.