Hi Dave
I had my Head unit changed as soon as I bought the car (could not get on with the little buttons) only thing I can remember of note was had to get a Harness adaptor think it was about a tenner from Halfords. must admit did not have DAB so cannot help with the aerial routing but with all the bits and pieces I have put on car since i found wiring routing to any where in/on the car is not much of a problem.
Good luck anyway
Steve