Oblgny, I would have to nominate the CS 2's as the easiest Thiel's to power (and most reliable):
https://www.stereophile.com/content/thiel-cs2-loudspeaker-measurements
Most of the earlier CS 1 series were amongst Thiel's easiest to drive as well.
Though the 3.5's impedance does climb just where the eq does it's stuff to help mitigate the eq's 12 dB's boost at the 20 Hz setting, well, that's still demanding of an amplifier.