Roasted Ducklings in Orange Sauce

Name: Roasted Ducklings in Orange Sauce
Ingredients: 2 ducklings, about 5 pounds each, giblets saved for the sauce; 1 tablespoon coarse salt; 1 bunch fresh thyme; 1 bunch fresh rosemary; 6 garlic cloves, peeled; 2 oranges, one quartered and seeded; the other sliced in 1/4-inch-thick rounds; 2 to 3 onions sliced in 1/2-inch-thick rounds; 1 bunch carrots, peeled and halved lengthwise; 1/4 cup Cointreau or other orange liqueur; 1 teaspoon salt; 2 teaspoons freshly ground black pepper; 16 ounces beef or chicken stock; Giblets and necks from the ducklings; 2 to 3 tablespoons rendered duck fat (from the roasting ducklings); 2 tablespoons all-purpose flour; 1/2 cup Cointreau or other orange liqueur; 1/4 cup red wine vinegar; 1/4 cup balsamic vinegar; 1/4 cup fresh orange juice; 1 cup orange marmalade; 2 tablespoons thinly sliced orange peel; 1 orange, sliced into thin rounds, for garnish