I did the 199mm upgrade with a kit from eBay, mostly because of the potential for an ABS issue, and a little bit because I didn't want to modify the dust shields.
It sort of makes sense that there could be issues with the 231mm calipers. They have larger pistons with larger surface areas. That means more force exerted or relieved on the pads/rotors for the same fluid pressure increase or decrease. The system is probably tuned for the swept area of the 199mm caliper pistons. In theory the control system should probably be able to still make the ABS work properly with the larger caliper pistons, but I didn't want to mess with it.