Combine water & bouillon cube in a heavy pot & bring to a boil. Stir in the rices & return to a boil. Lower heat, cover & simmer for 45 minutes, until the water has been absorbed. Let rices cool to room temperature.
Slice all the mushrooms & sweat them in a skillet over moderate heat until they are just wilted. Combine in a large mixing bowl with the rice & add remaining ingredients, including vinaigrette. Cover & marinate for 2 hours before serving. If making ahead, put in fridge & take it out 1 hour before serving.
VINAIGRETTE: Combine all ingredients in a cruet & shake till combined. Shake well before each use.