Its probably better to ask in the Alpine thread. There is lots of info on there and it gets answered to really quick!
With the E90 the foam is already included in the car and will house the tweeter.
With E92 you will need to purchase the grille/corner triangles they are different to the all around surrounds needed for the E90.
I don't have the P/N but if you order the Alpine kit from your vin number it pops up with the other two grille/triangles on their system.