Preheat the oven to 375°F. Lightly grease a 12-cup standard muffin pan or enough mini muffin pans for 48 muffins.
In a large bowl, whisk together the milk, eggs, melted butter, and maple syrup. Add the pancake mix and stir just until combined; a few small lumps are fine. Fold in the cooked, crumbled sausage and cheddar cheese.
Divide the batter among the prepared muffin cups, filling each about three-quarters full. If baking in batches, refrigerate the remaining batter between batches.
Bake standard muffins for 18 to 20 minutes or mini muffins for 10 to 12 minutes, until lightly golden and a toothpick inserted into the center comes out without wet batter.
Let cool in the pan for 5 minutes, then transfer to a wire rack. Serve warm with additional maple syrup, if desired.