Place salmon in shallow pan. Add water to cover, plus 2 cloves garlic, dill and 1/4 teaspoon salt. Bring to a boil; reduce heat to simmer. Cover and cook 3 minutes. Remove from heat and let stand in covered pan 8 minutes.
Heat broiler. Remove salmon from cooking liquid and place, skin side down, onto broiler pan. Baste with glaze. Broil, basting often with glaze, just until golden and well-glazed, about 2 minutes.
Glaze: Combine syrup, water, ginger, 4 cloves garlic, horseradish and 1/2 teaspoon salt in a small saucepan. Bring to a boil; reduce heat to simmer. Cook until reduced by half, about 15 minutes. Glaze will keep refrigerated for several days.