Heat olive oil in a large pot or Dutch oven over medium-high heat. Add the diced chicken breasts and cook for about 10 minutes, turning once, until beautifully cooked through.
Carefully remove the cooked chicken from the pot and set it aside for a moment.
Add both types of sliced mushrooms to the pot and sauté for roughly 6 minutes until softened. Remember to set aside a small portion of these cooked mushrooms for a lovely garnish later.
Stir in the finely chopped onion, minced garlic, dried thyme, ground marjoram, and grape juice. Continue to sauté for about 5 minutes until the onion is tender and fragrant.
Pour in the chicken broth and bring the mixture to a gentle simmer. Return the cooked chicken to the pot, give it a good stir, and let it simmer uncovered for about 10 minutes, allowing the flavors to meld beautifully.
Finally, add the cream cheese, Parmesan, and cheddar. Whisk gently until all the cheeses are melted and thoroughly combined, creating a creamy, luscious soup.
If you set aside any mushrooms earlier, quickly pan-fry them now to prepare your garnishes.
Serve your delightful soup warm, garnished with the pan-fried mushrooms, a sprinkle of extra shredded cheddar cheese, and fresh chopped parsley. Enjoy!