Shot in the dark here, but maybe one of the resistors in the crossovers was damaged somehow and its sending a full range signal to the tweeter? It would definitely cause massive distortion, but after looking at the speakers I'd be hard pressed to go that route. The crossover network is contained in the woofer. Who knows, I'd try hooking them up as the rears and see if you still get distortion. Could be a headunit issue.