Passive crossovers can also be "line level", in which case the benefits of bi-amping still apply (amplifiers direct to speaker drivers). The line level crossover is inserted between the preamp and power amp. The jury is still out on which of these methods (active or line level passive) is the preferred approach from a sonic standpoint.
The line level passive approach benefits from the fact that the crossover is working into the stable and high-ish input impedance of the power amplifier and, no additional active circuitry is involved that could contaminate the signal. The chosen components that make up the line level passive crossover can be smaller, less expensive and be equal or better quality than the larger speaker level crossover components that are working into 4 or 8 ohms.
The active approach benefits from the ability to better and more easily define the individual filter characteristics, such as the filter type, slope, transient response, passband ripple, phase & group delay, etc., with readily available components. When properly designed and implemented for a given speaker the results can be startlingly good. But too often active crossovers employ the simper filter types employing op-amps and the usual mid-fi componentry. So some of the theoretical benefits of the active crossover are compromised (a bit more noise, somewhat limited dynamic range, some electronic signature on the sound, etc.).
Today we also have outboard digital crossovers and equalizers, i.e. Behringer, XTA and BSS units. These loudspeaker management devices are competitively priced and offer quite a bit of promise for the engineer or hobbyist. One can use this equipment to obtain the very best crossover characteristics for a given loudspeaker then, either continue using it as the active crossover or, build an equivalent line level passive crossover that employs the optimum filter characteristics derived from experimentation. Or, even build a minimalist active crossover with the derived optimum characteristics.
Anyway to get back on subject, being a minimalist, I tend to think the line level passive approach has the edge unless a lot of effort and diligence goes into the circuitry design of the active crossover.
