It doesn't seem to work with the arena, so there's no point in using StartCombat. And I also read in the manual that it's impossible to influence the music played in the game. Without that, there's no point in setting a specific arena.
Although... You somehow managed to set the AI music in "Warlord". Could you share how you did it?
To be honest, from your debate with Ment, I still don't understand what task you're trying to solve. I used to insert "the right" music into the game (using a mod), and Ment subsequently used a similar method to insert music into his map.