The Dura-Ace ST9071 11-speed brake/shift levers attach to a TT/Tri base bar (aka as a bullhorn) to provide braking and perhaps more importantly an alternate location to make shifts. More locations to shift from means you can always be in the most efficient gear and there is no struggling to get back on the aero bars to make a shift. This can save lost time and also increase safety because the times you are on the bullhorns are generally for turns, climbs, bad pavement and crosswinds -- when shifting from an aero bar may to be the safest idea.
ST-9071 TT/Tri reverse levers have built-in E-tube wires with no additional E-tube ports. They required an inner bar diameter of 19.0 - 22.5mm and an outer diameter of 22.2 - 24.0mm.
All Di2 components on the bicycle require the same firmware version. Using Di2 components with different firmware versions may cause malfunctions. Use Di2 system checker to update component firmware from http://e-tubeproject.shimano.com/