Matching the ohms

Almost every enthusiast would like to replace the tape/radio in his Mercedes. This is very easy to do but involves also changing the ancient, paper-faced o.e. speakers as well. All aftermarket CD head units have four ohm speaker outputs, and all amplifiers which might be wired between the outputs of the head unit and the speakers, also have four ohm outputs. The o.e. speakers are nowhere near four ohms and should be replaced at the same time with same size coaxial speakers. The difference in sound quality would be incredible as well as the dynamic range provided by Compact disk and not existing on cassette tape. P.