I believe that both of the drivers are proprietary to Spendor, and it is likely that special cement and jigs are needed for assembly. That is probably why they want to sell you new drivers.
Considering the original cost of the speakers, probably at least $5000.00 dollars when new, $1500.00 is really not that bad to replace four of the six drivers.
Considering the original cost of the speakers, probably at least $5000.00 dollars when new, $1500.00 is really not that bad to replace four of the six drivers.