Preheat your oven to 350°F (175°C). Grease and flour three 8x2 inch round cake pans for even baking.
In a mixing bowl, combine the dry ingredients: sifted cake mix, flour, sugar, and salt. Whisk for at least 30 seconds to blend thoroughly. (If using cherry jell-o powder instead of cherry extract, add it here.)
Add the remaining ingredients – eggs, sour cream, vanilla and cherry extracts, oil, milk, and ⅔ cup of cherry juice from the maraschino cherries. Mix on medium speed for about 1 minute, then scrape down the bowl sides. Mix for another 1-2 minutes, or until smooth (extend mixing time slightly if using a hand mixer). In the last minute, fold in the chopped cherries.
Divide the batter evenly between the prepared pans and bake for 25-30 minutes. Check for doneness by inserting a toothpick into the center; if it comes out clean or with a few moist crumbs, the cake is ready.
Let the cakes cool in the pans for 5-10 minutes, then turn them out onto cooling racks to finish cooling completely.