Preheat the oven to 350F. Grease a 9x13" baking pan. In a large bowl, toss together the apples, pecans, both sugars, cinnamon, salt and vanilla. Then spread them out into the pan. Sprinkle the dry cake mix evenly over the top of the apples and place the butter cubes evenly over the top of the cake mix (be sure to cover the whole top with butter so you dont end up with any dry spots).