You could mount the MUD edition flaps to the XXL fenders. We have done it, but do not advocate that you do it as the extended fenders cause all the geometry to change and the angles on the flaps end up not matching as well as what they were designed for. Though you could theoretically install them to the Polaris XXL flairs, we cannot provide any support from our end that can help you install them correctly.
However, the Original version flaps CAN mount to the XXL flares and this ends up looking pretty good. It would add a bit more width close to the tire.
Both of these approaches are suitable if you are up for the task. Let us know if you decide to do it so that we can pass the info along to other RZR owners.