10-08-15: Doug99Actually the crossover - internal wiring and a new doping on the tweeters was the MKII/Signature changes (and the finish). With the Platinum they only changed the baffle to all black and jacked up the price. So the MKII/Signature/Platinum all sound the same but better than the originals. The difference is the original needed to be turned way up to sound the best whereas the newer ones sounded better at lower listening levels.
From what i read, the crossover is different.
That said the originals did play a bit louder when cranked to the Max.