I bought the drivers myself from Parts Express with the Jupiter Caps and Mills resistors from Partconnexion.  All said and done it set me back roughly $845 on my own.  ZU wants $700.00 just for the drivers, stating how they are matched, but really, I am spending $150 more with them for "matching".  Nevertheless, the upgrade is 100% worth it, I would do it again in a heartbeat, no comparison versus the little 1" Eminence drivers.  Add a terrific tube preamp and you are in sonic heaven.