Make the bean mixture: In a large heavy kettle combine the broth and the water and bring the liquid to a boil. Stir in the beans, the salt pork, and the sausage and bring the liquid to a boil, skimming the froth. Stir in the onions, the garlic, the thyme, the bouquet garni, and pepper to taste and simmer the mixture, uncovered, for 1 1/2 to 1 3/4 hours, or until the beans are tender. Discard the salt pork, the onions, and the bouquet garni, strain the mixture through a colander set over a large bowl, and in separate bowls reserve the bean mixture and the broth. The bean mixture and the broth may be made 1 day in advance and kept covered and chilled.
In a large skillet cook the bacon over moderate heat, stirring, until it is crisp and transfer it with tongs to paper towels to drain. In the fat remaining in the skillet brown the pork and the lamb over moderately high heat, turning the pieces once, for 8 minutes and transfer the meat with a slotted spoon to a large casserole. In the fat remaining in the skillet cook the onion, the celery, and the garlic with salt and pepper to taste over moderately low heat, stirring occasionally, until the vegetables are softened. Stir in the wine and boil the mixture until the liquid is reduced by half. Stir in the tomatoes with the reserved juice and the bacon and simmer the mixture, stirring occasionally, for 5 minutes. Transfer the mixture to the casserole and braise it, covered, in a preheated 325 degree oven for 1 hour.
Arrange the duck pieces, skin sides down, on a rack in a roasting pan and broil them under a preheated broiler about 4 inches from the heat for 10 minutes. Turn the duck pieces and broil them for 10 minutes more, or until the juices run clear and the meat is cooked through. Transfer the duck with tongs to a cutting board and reserve 1/4 cup of duck fat.
In a 6-quart casserole layer 1/3 of the reserved bean mixture, 1/2 the braised meat mixture, 4 pieces of duck, 1/2 remaining bean mixture, the remaining braised meat mixture, the remaining duck pieces, and the remaining bean mixture. Pour 6 cups of the reserved broth, skimmed of any fat, slowly over the mixture, sprinkle the top with 2 cups of the bread crumbs, and drizzle it with 2 tablespoons of the reserved duck fat. Bake the cassoulet, uncovered, in the middle of a 325 degree preheated oven for 30 minutes. Press the crumb layer lightly into the cassoulet, top it with the remaining 1 cup crumbs, and drizzle the top with the remaining 2 tablespoons duck fat. Bake the cassoulet for 1 3/4 hours more, until the crust is golden brown.