Re: rex in terri
I have the REX. It is a good unit but it and yes you can run head phones with or without speakers.
My REX makes a hum when you play DVDs through the speakers which Ford reckons is normal - I don't think it is but get your dealer to demo it for you first.
The REX is region 4 only which means you can't play imported DVDs which is a pain if you buy from Amazon etc.
In hindsight there are probably aftermarket sets that are as good or better and some even include TV tuners for half the price or less. These can all be hooked up to the stereo head unit by any smart installed as the inputs are all there.
I'd probably go for aftermarket unless they give you a real good deal on the REX.