if the 16 sz follows form/function with the 18 sz, you can assign channels in the function menu. the radio may already have a throttle 2 function available that you can assign to ch 9
you can do switch position assignments in the afr menus and in the p-mix menu
probably need to build a set of p-mixs to do the center both, left back, right forward.

about all i can help with, having to go by memory, as i am working remotely(as in a long way away from home and the radio to look at).