I've used Prima Luna Dialogue Four, custom built 300B SET monoblocks and Coincident 845 SET amp with my Klipschorns which has impedance drop to around 3 ohm at 100hz, sensitivity is higher at 104db. I've also auditioned Music Fidelity M2SI and Denafrips Hyperion amps, both class a/b solid state.
All have handled the impedance drop just fine. I do prefer tubes with Klipschorns, and expect all Heritage line better with tubes. As for sound quality, my favorite amp with the Klipschorns is the 300B's, sweetest sound which compliments Klipsch inherent qualities best. The one issue I could see in running 300B amps is handling your impedance curve, my 300B's monoblocks each have power supply equivalent to what one would normally see in stereo 300B, so no issues for me. 845SET should be no problem, and the push pulls fine as well.