i have an '06 JCW Checkmate with the Chrono pack and am wondering if its possible to swap the useless center gauges to an OEM Nav unit?

FYI: the car also has Harmon Kardon

 

Best option would be to buy a GPS if you don't gave a smartphone. Very costly and difficult to do. Dealer would probably do it for a huge price. You would need to buy a unit from them so it could be coded. Your center chrono unit is coded to the vin of your car so mileage will never be acurate.
I tried to do chrono to big speedo swap with incomplete success. Most things worked fine but others no so much.

 

Buy an aftermarket GPS...or better yet a large phone and a mount ...
The GPS from gen1 cars dates back to pre 2002.(car tech tends to lag by 3-4 years due to design cycles)...very dated...PRE DVD for many till they were updated to use DVD based maps.....and even those maps are getting dated.....heck MANY of those 10+ year old units are failing...hot, cold in a car...heck know of many 10 year old cell phones still in use?! Lol.
Not just as simple as yanking one part either.... The speedo and tach units are different part numbers since the arrangement of warning lights are different....
IMO consider yourself lucky you have working guages as opposed to idiot lights like other mini's....and a black screen like the ones with failed nav units....