[Pepppie]

Thanks for your reply! About the costs; I can get the whole Audison-system (amp+front+back+subs) for around 980 euro's. So that's a lot less comparing to the price in the US!

The advantage of the Audison-system is that it's all plug and play and it's all 'designed' for upgrading the hifi-system / 676-option.

But maybe there are better solutions for this price?

EDIT: Since my car doesn't have stock tweeters, I need to replace the windows-strips to get space for the front-door tweeters. Is there a huge difference in sound quality between the comp K4E and the coaxial X4E? Maybe it's an option to replace the OEM speakers with the X4E coaxial in stead of getting new parts to mount tweeters.