Stir together first 10 ingredients until blended.
Remove leg quarters from ducks; refrigerate breasts. Sprinkle quarters with 1/4 teaspoon salt and 1/4 teaspoon pepper, and place in a deep roasting pan. Add half of juice concentrate mixture; reserve remaining mixture.
Bake, covered, at 275° for 4 hours or until meat pulls away from bone.
Sprinkle duck breasts with remaining 1/4 teaspoon salt and remaining 1/4 teaspoon pepper.
Prepare fire by piling charcoal or lava rocks on each side of grill, leaving center empty. Place a drip pan between coals. Coat food rack with vegetable cooking spray, and place on grill. Arrange breasts, skin side up, over drip pan. Grill, covered with grill lid, over medium-high heat (350° to 400°) about 45 minutes or until a meat thermometer inserted into thickest portion registers 160°, basting occasionally with reserved juice concentrate mixture.
Turn breasts, and grill over direct heat 5 minutes or until crisp, basting occasionally with remaining juice concentrate mixture. Serve duck with Parsnip Mash. Garnish, if desired.