If you go for "ends (aft > fore)", it should indeed be 3 superfiring turrets.
Alternatively, if you have the weapon slots available, you can go for a 2 superfiring option like this:
a) Set the midbreak where it should be, between turrets Y and Z.
b) Sim 4 turrets using the 1st weapon slot and select "grouped forward" with two of them superfiring.
c) Sim 1 turret using the 2nd weapon slot and select "grouped aft".
I would have the forecastle break ahead of Z though
Uhm... I don't think you want to use the forecastle break... Don't you mean midbreak?