2005 Suburban Navigation Radio

I just purchased a used 2005 Suburban with the Navigation Radio in it. The problem seems to be that when the navigation DVD Rom is in the radio I cannot play cds. Is there a GM cd changer that I can get for this Suburban that will work with the Navigation radio? I see a few unused spaces just below the middle of the dash where it seems made for mounting something like that. Also, is there an AUX type of outlet on this radio for MP3 players?

One more item, a few of the buttons on the navigation radio have some of the paint chipped off or worn off. Is there a recommended fix for this? I don't suppose they have new buttons available or touch up paint, do they?

Thanks for the help in advance!

Slim