Help installing aftermarket DVD headunit

Hi,

I would like to get the in-dash dvd/mp3 player, with a seperate screen located in the center roof area. Can I still keep my stock 6-disc player and install the in-dash DVD player unit as well? Do I need some sort of splitter...for example when the stock unit is on, the in-dash DVD player can not turn on, and vice versa.

Thanks in advance.