Stir the brine ingredients together until salt and sugar are dissolved. Peel and devein the shrimp (reserving the shells) and place in brine for 1 to 2 hours refrigerated. Drain, rinse and set aside.
In a heavy saute pan heat 2 tablespoons of the butter and 1 tablespoon of oil over moderately high heat. Coarsely chop the reserved shells and add to the pan along with the shallots and stir until lightly colored. Add the vinegar and stock and reduce over high heat until sauce thickens slightly, about 4 minutes. Strain, pressing down on the solids and return to pan with the cream. Reduce again to a light sauce consistency. Stir in fruit, herbs and season to taste with salt and pepper. Set aside and keep warm (can be made ahead and gently reheated).
Wipe out pan, add remaining butter and oil and quickly saute shrimp until pink and barely cooked through. Arrange on warm plates, spoon warm sauce over and garnish with herb sprigs. Serve immediately.