Which stages of the fight have you gone through? You fight him initially (1/2 unarmored and 1/2 armored), do the running toward the camera sequence, then finally kill him in the other room when he comes out of the floor. There's also a QTE with button mashing at the end. If you are past the last part, did you try hitting R3? That will usually direct you when you're lost.

Bump. This is the only way I have figured out to switch as well. Same with switching back to the Game Pad from the Pro. Must be a weird operating system glitch.