As for the shunt resistor, I'd use a non-inductive resistor, 2x to 4x the Rdc of the driver. On some drivers it's more important, some less, but it cannot hurt to have additional damping. Values in this range won't reduce impedance much at all, but will give additinal damping. That's important when there is a capacitor in the circuit, because the voice coil is inductive and the two combine form a tank circuit. The shunt resistor helps damp the resonance.