I just had a "top of the line" Alpine/CD/MP3 stereo installed in my 560SEL which I purchased from Circuit City and installed by them. May I suggest you save yourself a lot of headache and aggravation and spring for the cost of installation by someone who will stand by their work to insure it is done correctly and offer a guarantee(installation guarantee, in your case). It is obvious you are a competent DIY'er judging by your previous posts and I hope you don't take this suggestion wrong, it's just that one's time has to be worth something as well as the outcome.
Cheers,
Gary
Cheers,
Gary