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.
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.
Heat griller. Remove salmon from cooking liquid and place, skin side down, onto griller pan. Baste with glaze.
Grill, basting often with glaze, just until golden and well-glazed, about 2 minutes.