I biamp with Sonogy amps for 220hz on down and Lamm ML1s above that, but I have an active crossover and a 4-piece system. There are always some potential sonic continuity problems, particularly with a crossover point that high, which are minimized by this combination, but I agree with Eldartford that the sonic characteristics of the amps, while potentially noticable, are not as big a problem as you might think. If you don't have an outboard active crossover you may run into amplifier input sensitivity and gain problems, though (for example, when I replaced my Jadis amps with the Lamms, I had to reduce the bass level on the crossovers significantly because the Jadis had a higher sensitivity, and thus subjectively played louder with less input, than the Lamms).
