I just checked my Music Reference RM-200 amp, and it has 8ohm, 4ohm, 2ohm, and 1ohm taps! It's a very stable circuit, and a good sounding amp. And the only tube amp I can think of that would work with the load of the Thiels. Give Roger a call and see what he thinks. He's an expert with difficult speakers, having designed the electronics for the Beveridge Electrostatics, and having a current direct-drive ESL/tube amp product.