Hi, the only way to change between the ARC mode and the 360 mode on the HSI is by the pop up 2d display? I mean it can't be done from the VC with the 3d switches?

I think you are right, the only way I know is the 2D-popup 

Micha, I'll be out of the sim for this weekend but a pilot friend told me about another way, go down on the bottom of the HSI gauge, on the VC, and switch between the "HSI" button and the "MAP" button (under the "- +" switch) in the HSI VC 3D gauge and you will find the same 2d clickspot switchable but from the HSI VC gauge. Can you confirm if it works on your system?