If I was the DA Chapter Master I would the bluff, get the entire DA chapter and the Unforgiven together and tear the strike force appart. I would advice that the strike force attacks without going over to the DA and tell them all about the plan. Ever read A Game of Thrones and the part between Eddard and Cersei in the godswood? Don't tell your plan to your enemies ahead of your execution of it.
It sucks for the DA, but attacking a Watchstation is pretty stupied so they pulled it over themselves, by their own hands.