Some good info above.
In absolutes, there is a possible benefit to passive biamping.
However, you're overwhelmingly better off spending the time and effort pursuing this toward learning more about room acoustics and the loudspeaker room interface.
fwiw, a segment of an old post of mine discussing this topic;
In the passive bi-amp situation, the load that each amp is presented with is reduced when compared to the total load on the amp in the single amp scenario. Load sharing. The inputs are paralleled, and that voltage is amplified, however it's where the current demands are different, that's where one could attain the small benefit.
The load on the HF amp; it possesses a high impedance at low frequencies, so it is easier to drive. As I understand it, the amp stages are boosting voltage, then the current is determined by the load at the terminals, and in this case the current demands are very low because it's amplifiying the upper portion, or the higher frequencies of the signal. Thus, not depleting the current reserves of the amp. High potentials can exist without current flow, it's the high current flow that saps everything from the output stages, the supply rails, and all the way back to the wall voltage during peak current demands. In this scenario, using a seperate amp for the high pass section, that huge current depletion doesn't occur.
Likewise, the amp supplying the low side of the crossover network, is presented with a high impedance above the pass band, so although the voltage amplification remains (parallel input), the current demands are reduced somewhat. Now obviously the dramatic lowering of current demands aren't the same in the LF amp as they are in the HF amp, but a reduction of the load is benefited by the amp, just a lesser degree.
Is it worth it, most likely not....Regardless, to state that there is no possible benefit associated with passive bi-amping, is in my opinion, incorrect.
Perhaps someone well versed in amplifier design can correct my in-accuracies, I'd like to now more about this as well.
The second benefit is the reduction of potential inter-modulation distortion, created in the LF section, and surfacing as distortion artifacts in the HF section. Very briefly, when transient drive voltage ceases at the LF driver, however the driver continues to move prior to settling, this generates a voltage. It is possible that this can contaminate the HF drive signal, if a low impedance path is present to ground (amp terminals), the corruption may be minimized.
Would I reccomend passive bi-amping? No, not if one has to buy gear to do it, it's hardly worth the trouble, even if you have the extra (identical) amps. Gain matching would be important.
There are many things of far greater importance, such as the speaker room interface, whereby one's attention should be focused for much more significant gains. That being said, I do welcome any input, or corrections.
Good luck to you