This question is really for my brother. He has a 2000 BMW 323ci with the factory stereo and speakers. He wants to switch all of the factory speakers for top of the line MB Quart speakers but he doesn't want to get an external amp. Will the speakers be any good without and external amp? Or will he have to get an external amp? Also he wanted to know he he could add an external amp to the factory speakers? I have no idea what the wattage is on the factory speakers but I'm sure they'll blow with an external amp but I need your advice to be sure what I should tell him.