To install the Dura Ace crankset you would need to have the shop press in a standard threaded BB adapter. You would then be able to thread in the Dura Ace BB cups. Once the adapter is pressed in to a carbon frame its not considered removable. (I have done it on my own bikes without issues, but you can void the warranty)
Its a tough call, the shifting on the new Dura Ace 7900 front is phenomenal, but you dont shift a lot up front in triathlons. I personally like the narrower stance of the BB30 cranks as I prefer to get my feet as close together as I can, but I have found some bigger riders prefer the wider stance of the Shimanos.
Kevin