Adding Lockpick & LCD Screens - Need Help With Choices

[430HP70]

im planning to add a lockpick and some lcd screens to the wifes 2011 yukon denali. it has the factory nav and the overhead rse. what im trying to determine is the best way to go about it. ive looked into the gmx550 and a pac audio cable for the rca outs, but im unsure if theres a better way. when i called coastal, i was told that i would need to reprogram the computer to get the rear screens to work. anyone know for sure? he said that there was no dvd out in the harness even though i have the overhead rse. another company i called suggested tapping into the feed at the current monitor and doing away with the pac module. but ive only found a wiring diagram for the NBS and the guy didnt have great results. what have others done? ive searched for hours with lots of info, but nothing that helped.

 

id also like some opinions on screens. id like to stay cheap since my kids dont really care about picture quality, but id like to mold them into the headrests. id like them to be a two piece design with a tray that gets attached, leather wrapped around and stapled and then the screen either snaps or screws into this tray. i did this with some invision headrests for my truck and it really cleans up the installation. everthing ive found so far has been either a screen or a full headrest, both which i would like to stay away from.