I have a 2006 GT with Shaker 1000 system, (and sub woofers in trunk). I want to replace the head unit with a doubble din DVD / GPS Nav system. What problems or issues will I have and how do I deal with them. I remember reading articles back when the car first came out - something about the subs in the trunk not working with other head units or problems with apms for the new head unit. I am not prificient with the electronics - swapped head units before but never build an entire system or anything. How difficult or easy would this be ? Any suggestions would be greatly appreciated. Thanks !