Preheat the oven to 375 degrees. Heat the olive oil over medium heat in a large saucepan or dutch oven with a tight fitting lid. Add onion and saute until soft and translucent, about 3-5 minutes. Add garlic and thyme and cook for one more minute.
Add barley, 3 cups of the broth and 1 cup of water. Bring to a simmer and then cover the pot and remove from the heat. Transfer the pot to the oven and bake until the barley is tender, about an hour.
Meanwhile, cook the mushrooms: Heat 2 tablespoons of olive oil in a large skillet over medium heat. Add the sliced mushrooms. Cook, stirring frequently, until the mushrooms are tender and browned, about 10 minutes. Remove from the heat and add the soy sauce, scraping up any brown bits that have accumulated on the bottom of the skillet. Season to taste with salt and pepper and set aside.
Remove the pot from the oven and transfer to the stove top. Turn the heat to medium-low. Add the wine and remaining cup of broth. Stir constantly until the ingredients are incorporated and the mixture is creamy, about 3 minutes. Remove from the heat and stir in the butter and parmesan. Season to taste with salt and pepper. Gently fold in mushroom mixture, including any accumulated juices. Top with chopped fresh parsley or chives if desired and serve immediately.