^ As I understand it most Thiel driver failures are the result of underpowered / overdriven use. Being mindful of Thiel's minimum impedance and the amp's ability to truly handle it, and you should be OK. Even with the 1st order cross-over overlaps, most Thiel drivers are quite robust, and can handle quite a bit of power.
The CS 3.5's mid-range replacements are a difficult find.