I have an 07 LTZ. It came with most options except it only has the 6 cd changer radio instead of a Nav system. It doesn't have a rear DVD either. I want to upgrade to a Nav system and maybe backup camera and I have found 2 different head unit part numbers. GM# 15882767 (for vehicles with out the rear DVD player) and GM# 1588766 (for vehicles with the rear DVD player). My question is can I buy either one for what my plans are or do I have to get the one for NO DVD player? I have seen both on Ebay.