I have actively bi-amplified my Magnepan 3-series using an external active crossover (Marchand). You have to have a decent crossover or it’s a waste.
My take was that the active bi-amping was a complete sea change in sound. As it should be since you are using an entirely different crossover network and the crossover is before and not after the amplifier, so the amplifier is freed to fully power the drivers it’s connected to. Worked very well.
But that’s because Maggies have that biamp capability without surgery. You have to take out the internal crossover network in speakers to do this right. With most speakers I’d say it probably isn’t worth the risk or effort. The speaker designer had the crossover network in mind. Magnepan clearly had active biamping in mind.
So, in limited circumstances it can be a huge improvement. But, limited circumstances. Biamping without taking out the passive crossovers is just a bit more oomph in power but at the cost of a lack of consistency. I wouldn’t do that.