In a stockpot over medium-high heat, sauté the shrimp and lobster shells until pink.
Add the sherry and white wine, and simmer until reduced, about 5 minutes.
Add the rest of the ingredients and enough water to cover, about 6 to 7 cups.
Simmer (do not boil) uncovered, for an hour, or until reduced to about 4 cups of liquid.
Strain through a fine mesh cloth. Discard solids.
For the soup:
In a large saucepan over medium heat, sauté the shallot in butter until translucent.
Add the sherry and simmer until reduced by half.
Add the tomato paste, tomatoes, stock, paprika and thyme. Simmer gently, covered for 20 minutes. Remove the thyme and puree with an immersion blender. Pass soup through a fine mesh cloth or sieve.
Return to low heat and temper the cream with some of the hot soup, and slowly add to the soup.
Add salt and pepper to taste.
Add the lobster and shrimp to the gently simmering soup.
Simmer for 3 minutes, turn off the heat and cover for 2 to 3 minutes more.
Serve immediately, garnished with a drizzle of chili oil, and a sprig of thyme.