Yes I would guess a capacitor in that crossover failed. If possible you might need to remove that crossover yourself and find someone online who can fix it.
There used to be a pretty big market for people building DIY "clones" of the Proac Response models. You might be able to find a hobbyist capable of troubleshooting it, even better if they are already familiar with the design. Sort of a longshot though. Good luck on the search.