I passively bi-amp with VTL MB100 tubes on the top and Sunfire Symphonic Reference on the bottom.
These amps are way out of gain match but I controll the gain of the Sunfire with professional ClearBock balanced line converter that I use to decrease the gain of Sunfire to match VTL.
Also VTL is connected to the high-pass(80Hz -3db and after 12dB per octave) output of preamplifier. THe benefit is to limit the "visible" freequency bandwidth to the amplifier thus significantly decreasing distortions that are quite big in tube amps in the bottom end.
These amps are way out of gain match but I controll the gain of the Sunfire with professional ClearBock balanced line converter that I use to decrease the gain of Sunfire to match VTL.
Also VTL is connected to the high-pass(80Hz -3db and after 12dB per octave) output of preamplifier. THe benefit is to limit the "visible" freequency bandwidth to the amplifier thus significantly decreasing distortions that are quite big in tube amps in the bottom end.