actually the NAV can be fixed. pressing the map button will bring the new system in. I do these for a living.
where are you?
theres not a lot thats NOT possible with these. I'm working on a cruise setup for these cars as well. it will take the place of the blank silver tabs on the wheel.
gauges are volt,boost and oil temp (unsure on the last one - I see more of the integrated dash cars.)
as for pulling the 6cd out and popping guages back in - yep VERY doable. the harness is there regardless of the dash fitted.