SL55/63/65/R230 AMG: Upgrading Navigation on 2005 SL55 AMG
They can do some amazing work. I'd shy away from the China drop ins you see. For every one or two that seem to get everything working great, 5 or 6 can't get certain things working. Plus even if your lucky enough to get it done and working, my guess is the sound quality is questionable at best.
Figure out what you want to spend and go talk to the car audio places and see what they can do for you correctly.
Also having an '05 SL means head unit trim pieces are available so you can make it look pretty well integrated with the dash.
Go see your local audio shop. I'm not sure some place like Crutchfield has items for our cars.


