Preheat the oven to 375 degrees F and butter a shallow 3-quart baking dish. Melt 6 tablespoons butter in a large nonstick skillet over medium heat. Add the scallion whites, bell pepper and celery; cook, stirring occasionally, until the vegetables are softened, about 6 minutes. Add the thyme and sherry and cook, stirring, until the sherry is mostly reduced, 3 minutes. Add the broth, 1 teaspoon salt and the cayenne; bring to a simmer, then remove from the heat.
Whisk the eggs in a large bowl and add the scallion greens. Add the bread cubes, vegetable-broth mixture and crabmeat and stir until combined. Transfer to the prepared baking dish. Cut the remaining 2 tablespoons butter into small cubes and scatter evenly over the stuffing; sprinkle with the paprika. Cover with foil and bake 30 minutes, then uncover and bake until golden brown, 20 to 30 more minutes.