Auto Assign Tasks

I am trying to create a workflow that will change an "assigned to" cell dependent on a number of cell that will be checked, for example:

If the product needs to be delivered to the customer then the "product sent" checkbox is blank triggering a " Assigned to Sales Person" if the checkbox is checked then the "assigned to" cell moves to "Project Manager". 

I can use a formula to complete this with a single task but not with multiple. 

=IF([Sample Request Submitted]1 = 0, "Sales Person", "Creative Services")

OR

IF([Samples Delivered to Sales/PM]1 = 0, "Creative Services", "Sales Person")

But I can't seem to combine them. Thanks. 

=IF([Sample Request Submitted]1 = 0, "Sales Person", "Creative Services"), IF([Samples Delivered to Sales/PM]1 = 0, "Creative Services", "Sales Person")

 - Eric