MBQuarts will only sound good if you add an amp to the system. If you do not want to do this then may I suggest getting the Polk 5" coaxials EX350 from crutchfield for the front and maybe a slim subwoofer to slide under the seat like the Kenwood KSC-WA62RC.
The back speakers take some work but you can order an exact replacement through a blaupunk dealer such as http://continentalimports.com/

Hope this helps these cars are a pain to upgrade...