After much deliberation I've decided to give the Discover Pro a miss and have just added the Dynaudio pack on it's own.
It's hard to justify spending £600/£700 to have a larger display,3D graphics, and a DVD player I will literally never use.
I hardly ever use a satnav as it is so simply having a built in unit is a bonus on it's own.
I'll probably spend the money I save on a new computer ( yes, that's how much they charge for a big screen satnav!! )