Coarsely grind the fennel seeds, peppercorns and coriander seeds in a spice grinder or with a mortar and pestle. Transfer to a bowl and mix with the salt, sugar and grapefruit zest and juice.
Place the salmon fillets side by side, skin-side down, on a large piece of plastic wrap. Scatter the salt mixture over and around the fish. Top one fillet with the dill, then put the other fillet on top, skin-side up. Pat any extra salt mixture all over the fish. Wrap tightly in the plastic wrap and put the fish on a plate. Cover with another plate and put 2 or 3 heavy cans on top to weigh it down. Refrigerate 2 to 3 days, flipping the salmon daily.
Unwrap the salmon and rinse under cold water to remove the spices and herbs. Pat dry with paper towels. Slice the salmon at an angle as thinly as possible with a sharp knife.
Before serving, press the egg whites through a fine-mesh strainer into a bowl. Repeat with the yolks. Arrange the salmon and bread on a platter. Put the chopped onion, chives, capers, beet horseradish and radishes in separate bowls for toppings.