can you put two after market audio head units in one truck and use the stock

[seniors07_12]

speakers for both? i've got a sony head unit now with an amp and two subs. what i want to know is can i splice the wires from the back of the sony head unit and hook up a international dvd player touch screen as well. i'll have a switch to supply power to another amp so i dont run my battery down. i just want to know if it will cause any damage