I want to add a sub and upgraded interior speakers. I have vast experience with high end stereos (i only use Alpine and Diamond Audio products). My question is, can i keep the stock head unit/Navi to run my stereo? Can i use the navi screen as a DVD screen? Thanks.

you can use your stock radio to hook up an amp all you need is a converter box that converts speaker wire into rca's as for using your nav screen as a dvd i doubt it but look for video inputs if you got one then get a dvd player or better yet a xbox 360