You will need the Ultegra STIs (one set) and the cable that connects the two (called handlebar harness) as well as some type of momentary switch for shifiting. You can use the DA di2 shifters as the momentary switches but you will still need the parts from the Ultegra STIs. Sorry, its a little confusing at first.

For shifting on the base bar, you can use any type of momentary switch also, even the DA brake/shifters...just wire them to the module the same way as the bar end shifters.