Me, on the speakers linked in my sig. Why? Because the tweeter's impedance chart and frequency response are pretty damn tough to shape using only cut filters that are impedance-dependant (passive crossover), especially near the crossover frequency. This is exactly why I passively bi-amped my original Legacy Focus. The three 12" woofers presented a <2 ohm load in spots below 200Hz, and seldom went above 3 ohms. Passive bi-amping sounded better to me in the mids and highs. Of course, the Focus also used 2x6.5" midrange drivers, a tweeter, and a super tweeter, and silly-complicated crossover. I've never heard another speaker before or since benefit from passive bi-amping, but I suppose these exceptions exist. In general I never recommend passive bi-amping.
