Multiple modifiers osascript / shell

Hi

Im trying to automate keyboard shortcuts and have got as far as working commands with single modifiers (CMD+C etc.) but can't seem to get any to work with multiple modifiers (SHIFT+CMD+S etc.). In terminal and script editor you simply use {shift down, command down} but in max that doesn't seem to work.

So far i've got : osascript -e 'tell application \"System Events\"' -e keystroke \"c\" using command down'   <<< that script will copy in any application you have selected.

Does anyone know how max does multiple modifiers??