>>569>>571
GamePadState pad1 = GamePad.GetState(PlayerIndex.One);
GamePadState pad2 = GamePad.GetState(PlayerIndex.Two);
GamePadState pad3 = GamePad.GetState(PlayerIndex.Three);
GamePadState pad4 = GamePad.GetState(PlayerIndex.Four);

if (pad1.Button.A == ButtonState.Pressed || pad2.Button.A == ButtonState.Pressed || pad3.Button.A == ButtonState.Pressed || pad4.Button.A == ButtonState.Pressed)
{
//Aボタンが押されたとき
}

これでいいだろ。差し替えにも対応してるし。