Ram,

Be smart and just get the OE headrest monitor, one one side only to do it cost effectively. The kids will get used to it. DVD sound to IR headphones via AUX in ala DICE. Simple run under the front passenger's carpet and through the seat to new headrest. IR trigger could be simultaneously run to the center dash for remote control from most 'qngles within the car.
I would use this route just so the little ones don't rip the DVD monitor off with their feet and your elbow won't hit it when you reach back there to smack one of them on long trips (haha). At the very least, when you sell the car the headrest is a simple remove and re-install the old one.

My worthless $.02 as usual................

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2010 Specialized Epic Carbon Comp XX
1976 FJ40 Toyota Landcruiser (SOA,350ci sbc V8 crawler)
2007 X5 4.8i
2008 Porsche Cayenne Turbo S