If you desire to use the WATCH Dog in a hybrid or multiple configuration system, then the external controller becomes the brains behind that flexibility, whether you're using one subwoofer or several.
The first thing to know about the WATCH Dog Controller is this: you may not need one. If your intended use for the passive WATCH Dog subwoofer is solely as an LFE (low frequency effects) driver in a 7.1 or 5.1 Home Theater system, all you need to do is connect the subwoofer directly to the LFE output of your amplifier(s) and be prepared for seat of the pants excitement in your home movie experience.
If you desire to use the WATCH Dog in a hybrid or multiple configuration system, then the external controller becomes the brains behind that flexibility, whether you're using one subwoofer or several.
In Movie Mode, the low frequency effects output from your processor goes directly through the controller to the WATCH Dog.
Switching to Music Mode (accomplished either with a front panel toggle or a 12 volt trigger), the controller becomes a feature-rich crossover and equalizer. You can control both crossover frequency and slope. A continuously variable phase control and EQ functions complete the features necessary to seamlessly integrate a WATCH Dog with any pair of Wilson loudpseakers.
More info - https://www.wilsonaudio.com/products/watch-controller