I'm in the market for a used 460 and looking at a very clean 2011 Premium model. When I was test driving it, the stereo sounded pretty good, but I forgot to look and see if the little badge behind the slide down cover said Mark Levinson on it. Does the Premium model always come with the ML stereo, or it is an optional add-on? This one also has the video screens facing the 2nd row seats. Not sure if that makes a difference. Thank you.