Surely they'd prep for both to some degree though? How do teams manage preparations during a season when they play one team on a Wednesday and then a different team on the Saturday?
It's been 9 days now since Hull got into the final and it will have been 12 days come the final. Surely they've had plenty of time to look at Southampton to be 90% ready. They could have also looked at Boro and today will probably focusing more on Boro in the run up to the final, more so if the appeal isn't successful.
I bet Hull prefer to play Boro anyway even though they've beaten Southampton twice this season. That was way back in September and January and Southampton are a much better team since then and now (spying aside).
Southampton won 8 of their last 10 in the league and drew the other 2. They also drew with and beat Boro in the playoffs. Boro won 2 of their last 10 league games and didn't win against Southampton. I know who'd I'd want to be playing in the final if it we were in Hull's position