I don't have any experience with this 16km mod,but i'd still put a bet on that the hydrophones will still be able to pick up sounds a lot further away.
The OS allows you to see more of your immediate viewing area compared to the PS,and the OS has less range than the PS.The PS can zoom upto x6,where the OS is x1.5 I think.
The only time I raise the OS when surfaced is when in rough seas and the waves are coming over the conning tower,it allows me to still be able to see as the boat goes under momentarily.
Is this what you wanted to know?
