I have a pair of 6.3i's and they are great speakers. It is my understanding that Phil Jones had the drivers custom manufactured to his design specs, as Jmbatkh mentions. If you do replace the drivers, chances are that changes will also be required in the crossover. I wouldn't pay more than maybe 10% of the MSRP, due to the fact that you will have to do a lot of homework to make repairs. I paid less than 22% of list for mine, but they were in mint condition.
Good luck.
Good luck.