This is actually a pretty easy mod. Takes around 30-45 minutes to mount the monitors in the headrest itself, overnight to let the foam cure, and 30 minutes of wiring to get the job complete.

Materials:
Expanding Foam
X-acto Knife
Monitors that fit your headrest
and umm... Headrests!



First step is to line up the monitor and mounting plate where you want it on the headrest.



Then pop out the monitor from the mounting plate, trace the outer edge of the mounting plate onto the headrest, but make sure to trace the part at the back , not the lip that will hide the cut edges.


Now draw an x from corner to corner on you headrest and carefully cut out that pattern.



Next comes the fun part. Carefully remove the foam from the inside of the headrest to make the pocket for the monitor. Your best bet is to cut down into the foam roughly the depth of the mounting plate along the edges and carefully pull out piece by piece. You need to make sure that you don't go too deep.



Test fit the mounting plate to make sure it will sit well where you want it a few times. You have a few options in securing the mounting plate to the headrest. You can secure it with cable ties to the bar within the headrest, or use a small plate and sandwich the bar between them and screw it in (personally i think that takes up too much space and removes too much foam). I went with the easiest method and cable tie'ed it in. Run a channel out the bottom of the headrest for the wiring, then run the wire. DO NOT put the monitor in the mounting plate yet. using the expanding foam, fill in all the spaces behind the mounting plate. Allow it to cure overnight, the foam will bond to the mounting plate and the old foam.

Now put the monitor into it's housing and pull the slack on the wire and voila! You now have a headrest monitor. All you have to to is run the wires and hook them into your video source. I have a video selector and a 1-7 video amplifier rather than using a bunch of Y splitters which will just degrade the signal the more you split it.

To get the wire down the seats, I cut a small x just big enough for the cable in the top of the seat nad will be getting a grommet for the hole later to prevent fraying. Then using fish tape (it's a hardware thing, any of you who have seen me at shows hooking things up have seen it, basically a wire strip with a hook on the end designed to pull wire through walls without cutting into the wall too much), pull the wire up the back of the seat and out the top.

Here's a shot of my finished product.






And for those that notice the difference in sizes, would you believe that hyundai makes front and rear headrest? I was planning on getting another set anyway, so that will balance it out.