Spray a 6-quart slow cooker with non-stick cooking spray.
Place pasta in a colander and rinse well in cold water; drain well. Add drained pasta to crockpot.
In a large mixing bowl stir together milk (2 1/2 cups), evaporated milk (12 ounces), condensed cheddar cheese soup (11 ounces), sour cream (1/2 cup), cheddar cheese (8 ounces), jack cheese (8 ounces), salt (1 teaspoon), black pepper (1/2 teaspoon), dry mustard (1/2 teaspoon), onion powder (1 teaspoon), nutmeg (1/8 teaspoon), and cayenne (1/8 teaspoon) until smooth. Pour over pasta and stir. Press down pasta, if need, to submerge as much as possible. Dot the top of the mixture with butter (1/4 cup).
Place cover on crockpot and cook on low for 1 hour. Remove lid and stir. Check pasta for doneness. If not done, cover and cook 1-2 hours more, as need, checking every 20-30 minutes, to reach the desired doneness of pasta. (Each slow cooker cooks at different temperatures!!)
Meanwhile, while mac and cheese are cooking, make the breadcrumb topping; Melt butter (2 tablespoons) in a large skillet. Add panko (2 cups), salt (1/4 teaspoon), pepper (1/4 teaspoon), and thyme leaves (1 teaspoon). Cook on medium, stirring frequently until crumbs are nicely toasted and crispy, Cool and stir in Parmesan (1/2 cup).
When mac and cheese are cooked, evenly sprinkle bread crumbs over top. Cover crockpot, set on keep warm for 5 minutes then Serve!