Will my existing RX-8 spark plug wires fit the AEM Smart Coils?

Usually not. Stock-type wires (including many aftermarket wires built to the stock coil terminals) have coil-side terminals for the factory coils and do not fit the AEM 30-2853. You can either order a new MSD wire set built for the AEM coils, or buy the correct boots and terminals and re-terminate your wires. The second option needs a special crimping tool and is more error-prone.