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There was a digital converter made that converts the MOST signals to a digital copper wire signal so that you can keep your existing MOST components working while using after market head units. I'll get you the rest of the information and how to buy the digital converter.
You can add just an auxiliary port that is compatible with your iPhone and mp3 players but more modern head units offer such better bluetooth, navigation and other features that it may just be worth it to get the converter and then a new head unit.
These are some suggested parts to use, The Nav-tv M.O.S.T HUR is the digital converter and it says its only compatible with S, CL, and SL classes because they have Bose amplifiers but they have been proven to work with the Harmon Kardon amplifiers according to various forums. All these components all cost you about $1300. I added a rear view camera for about $100 and the steering wheel control adapter for $50 but it may be a lot more for installation. The MOST converter and head unit are $550 each. If you wanted to go just the auxiliary input device, its about $500.
Kenwood DNX7190HD Nav-TV M.O.S.T HUR MB “OPTI-1” Kenwood CMOS-210 Universal Rear view camera 40-EU10 antenna adapterAxxess ASWC-1 Steering Wheel Control Universal
If you could post your VIN#, I just need to confirm you have the option harmon kardon amplifier. If you don't have that option, then you wouldn't necessarily need any of this stuff because the new head unit can just power up the speakers directly without the use of MOST converters. You would lose your CD changer of course but thats a small price to pay for a modern head unit with tons of features.
Yes, sorry it took me a while to respond. Your car is equipped the extra amplifier run by M.O.S.T. so the M.O.S.T Hur unit will have to be test fitted to make sure it operates. I know it sounds kind of dodgy but that is what the factory instruction booklet says to do. I'll give you some links on the instructions and where to purchase the unit. I suppose if the unit wasn't compatible with your vehicle, you could always return it for a refund. https://navtv.com/products/NTV-KIT421/most-hur-mb-opti-1.html There are downloadable instructions in that link, I have read on other forums that this unit works with most other vehicles with a M.O.S.T amplifier which is what you have. If you don't want to go through the hassle of actually having someone try and do this, then I suggest you just get an auxiliary cable adapter like this one. https://navtv.com/products/NTV-KIT002/most-aux-mb.html
There is one last cheaper option, You can retrofit an auxiliary jack into your glovebox just like the factory. The parts are relatively inexpensive but you have to add the cable for the auxiliary phone jack into the back of the COMAND head unit. Here is the link for the webpage that has links for instructions. Any car audio shop should be able to do this for you with the information on this website. http://www.mercupgrades.com/Aux+input+retrofit+on+A+B+C+CLK+ML+GL+R-article-17.html
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