1. Drain peaches reserving syrup for sauce.
2. Combine 4 oz. unsalted butter, brown sugar, reserved syrup from peaches, and evaporated milk; cook over medium heat until syrupy, about 5 minutes; set aside.
3. Preheat oven to 325°F. Use remaining 2 Tbsp. butter to grease 13x9x2 inch baking pan.
4. Pour caramel sauce in pan, and arrange peaches over bottom; sprinkle with cinnamon and chopped pecans.
5. Prepare cake mix according to package directions; pour over fruit. Bake 30 minutes.
6. Cool completely before unmolding. Serve with ice cream and additional sliced peaches, if desired.