1. All MoGraph -- Blend between cloners:
In this method you create a cloner that represents the low clone count and duplicate it, setting the clone count to the maximum number you want. Then you put both of them in another cloner set to blend mode. Apply the sound effector to this clone and in the parameters tab turn "modify clones" up to 100%.
2. MoGraph + Xpresso:
With this method you create an Xpresso expression with four nodes. Drag in the sound effector and connect its object port to a mograph>Data node's object in port. Add an out>strength port the data node and connect it to a range mapper. Adjust the range mapper parameters and connect it to the cloner's clone count in port.