I have a '06 and can't seemed to get the rear head retraints out either. I start by bringing them all the way up and then pulling. It doesn't feel 'right' so I've stopped before something breaks.

My reason for removing the center HR is different. I have this neat clear thin piece of plastic that works like a fish eye. When properly placed, it alows you to almost see within 1 foot of the rear bumper. Really makes parking easier.