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.
To prepare salmon:
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.
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.
Makes 4 servings.