Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a mixing bowl, beat together the cream cheese, ½ cup of granulated sugar, and a pinch of salt until smooth. Add in the 2 large eggs, 1 cup of sour cream, and 1 teaspoon of vanilla extract, and mix until fully combined. Pour this mixture evenly into the prepared cake pans and set aside.
In a separate bowl, whisk together the flour, baking powder, and 1 teaspoon of salt. In another bowl, cream together 1 cup of unsalted butter and 1 cup of granulated sugar until light and fluffy. Add in the 3 large eggs, one at a time, mixing well after each addition.
Alternate adding the dry ingredients and the buttermilk into the butter mixture, starting and ending with the dry ingredients. Mix until just combined. Stir in the lemon zest, lemon juice, and lemon-lime soda.
Pour the lemon cake batter over the cheesecake filling in both pans, filling them about ¾ full. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Allow the cakes to cool in the pans for 10 minutes before transferring to wire racks to cool completely.
In a mixing bowl, beat the 6 ounces of cream cheese and 1 cup of unsalted butter until smooth. Gradually add in the powdered sugar, mixing well. Then, add the lemon zest and lemon juice, adjusting as necessary for flavor and consistency.
Once the cake layers are completely cool, place one layer on a serving plate. Spread a generous amount of frosting on top, then add the second layer of cake. Frost the top and sides of the cake until fully covered.