There are a number of sets that have optional bonuses if you have a shield for the set. Brig armor is a good example. So, do you have to have a +6 shield to get the +6 bonus or not?
in the description of the set, it says "with a shield..." although i can see how this can be misleading, what it means that there is an additional sort of set bonus with that set if you also have a speciffic shield equipped. you will still get the original set bonus with just +6 non-shield set. i am not sure, however, the order in which the set bonus, shield bonus, and +6 bonus are applied. (so +6 may not effect a shield at all)