I have been using Big Hattor Dual mono (AMRGtrans, active phase of NewClassD for two years now - but I usually listen in passive mode) in conjunction with the SimAudio Moon W8 power amplifier. It suits me perfectly. Compliance with the input impedance of the amplifier is an important consideration for operation in passive mode.
Hattor Audio preamps?
Got my eye on one of these. And yes, my system is passive friendly. I've had resistor based passives before, as well as transformer, autoformer and LDR preamps. So I know I like the sound quality which can be had with a passive. Anyone out there have any experience with the Hattor stuff?