For the grits: Bring 2 cups of the chicken stock, the heavy cream and 4 tablespoons of the butter to a simmer in a heavy saucepan. Gradually whisk in the grits. Reduce the heat and simmer until the grits have thickened, 15 to 20 minutes, stirring occasionally to avoid lumps. Once the grits are thick and creamy, adjust the consistency with stock, if necessary, and season with salt and pepper.
For the shrimp and sausage: Heat the olive oil in a large skillet. Add the sausage and brown, then transfer to a plate with a slotted spoon, leaving all of the fat in the pan. Add the garlic, bell peppers and onions. Sprinkle with salt and pepper and saute until tender, 5 to 7 minutes. Add the shrimp and Cajun seasoning to the pan and saute until the shrimp are beginning to turn pink, 1 to 2 minutes. Add the reserved sausage and remaining 1/2 cup chicken stock to the skillet and reduce a bit to intensify those flavors. Stir in the remaining tablespoon butter at the end, garnish with parsley, and add the lemon juice.
Serve the sausage, peppers and shrimp over the grits.