The Ohm rating is a nominal one, not necessarily one that repeats it's impedance over the bandwidth of the driver in it's application. Furthermore, Jim Thiel designed his cross-overs to compensate for specific driver anomalies. Those specially designed cross-overs might alter the non OEM drivers in areas where they don'[t need it, and not alter them where they do need it.
Either call Thiel for driver replacement or rebuild, or call Bill LeGall of Miller Sound for excellent work on driver rebuilds, just explain the situation.
Anything less will undo Jim Thiel's hard work and you'll could be left with a Frankenstein butcher job that might seriously compromise the resale value of the speakers.