The PO of my 560sl installed an Eclipse unit which functions very well and has a one disc slot. Here is the web site of the company -- its a Fujitsu company.
http://www.eclipse-web.com/
My unit looks a bit more conservative than some of their higher end units -- I figure its at least two years old. It is my understanding that the local MB dealership installed it in the car. -- Take a look at what they have.