The day before, mix and shape the cakes, and make the sauces. Sauté the cakes one hour before the party; cover and keep warm in a 200° oven.
Process scallops in a food processor until chopped. Add cream and next 4 ingredients; process until combined, stopping to scrape down sides.
Combine scallop mixture, onions, and tomato; gently fold in crabmeat. Cover and chill at least 2 hours.
Shape mixture into 8 patties (about 1/3 cup each).
Melt butter in a large skillet over medium-high heat; add cakes, and cook, in batches, 3 to 4 minutes on each side or until golden. Serve with Red Pepper Sauce and Yellow Pepper Sauce; garnish, if desired.