Lexus used their subcontracted A/V specialist to replace the DVD system. They ended up replacing the entire system including all wires, control board, both monitors etc... This involved removing both front seats and the center console (as the wires run into and up under the console). I was very concerned about the possibility of squeaks/rattles post repair but have had no issues. I looked into the 1st owner's service records and found that the Invision DVD system had been previously replaced by a different Lexus dealership several years ago, so now it is on DVD system #2 @ 75K. Neither myself nor the original owner has young children and as such the system is never used.
If I had to of paid for it out of pocket, I would have replaced the control board and the left headrest monitor and called it good. Hopefully yours won't need such an extensive repair.
Be sure and check the 6-pin connectors on the bottom of the seat backs and check the control box under the passenger seat.