I agree that the DO can extend you, but you have rights under the contract as well.

If you are suppose to end an 11 hour duty day in LAX and upon arrival are told that they are going to turn you in two hours and then operate back to MEM, and the DO has approved it, would you say ok? I would contact the DO. I would explain to him that I planned my sleep on an 11 hour duty and that I don't feel it is safe to extend past the operational extension. If they can turn us quick enough to stay within the operational duty extension, I will give it a try, otherwise, I would like to go to the hotel. I would then reference the appropriate section of the contract.

If you simply ask the DO or CE whether the DO can extend you to 16 hours or not, then the correct answer is yes he can. We (pilots) need to go the extra step and ask the DO to exercise the two options available in the contract if we don't feel we can safely go beyond an operational extension.

Take it for what it's worth. I am not going to make my decisions based on what anonymous posters (myself included) on a forum tell me to do. I am going to reference the contract, and if needed, call CE.