Given the fact that slight audio tweakes proved to work perfectly if done carefully, I guess you could replace the line
"you can't win Darth" with "you won't win...darth"
Putting you won't win Darth gives a sense of plan to OB1's action; as someone said, he's already thought of a possible encounter with Anakin. And the pause before Darth would be just an idea to make the whole thing a little more ironic following Kenobi's prequel style, and a nice solution to the thing of Darth being Vader's first name.