Bose speakers and factory GPS in CLK

A friend of mine is about to take delivery of a 2000 CLK. My knowledge is not that geared towards new-fangled cars, where everything is
electronic and little is user-serviceable. ;)
The car allegedly comes with BOSE speakers, but has a (broken) aftermarket GPS head unit. I would imagine the BOSE system is some kind of proprietary thing, with a hidden amp and maybe integration with a specific head unit? Am I way off target?
What's the easiest way to tell if this system is/was fitted?
Another question - how difficult is it to retro-fit the factory GPS unit if the car didn't come with it? Is the loom in place? Is there an external aerial? I saw a couple on ebay and I would imagine that breakers must have more.
Sorry for my lack of knowledge, and any links to the nitty-gritty of these cars are most welcome.
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