Am I wasting money on the theory of Bi-amping?

NO! Because it is NEVER the THEORY that is the waste of money. It is always the application / implementation of the flawed theory that is a waste of money. Notice that all these other posters with multi-paragraph theories aren't wasting one dime of their money with their theories.

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.

I biamp in one of my systems.  I use a pair of mono amps to handle the bass and a different pair of mono amps to handle the mids and highs. The mid/high have the bass rolled off using high quality caps at the amp inputs and there is an adjustable unit to balance the bass (which goes through untouched) with the mids/highs.

This is the system that Richard Vandersteen uses and it works very well with my big Vandersteens, although many would prefer to avoid the complexity of four mono amps with an external adjustable crossover for the bass.

Does it sound better done this way?  I was pleased to find that it does and the improvement warranted the extra system complexity.

Whether you would get the same gains depends entirely on your particular system.

Seems biamping in an ideal way would be using a tube amplifier for upper drivers, and solid state for bass. I believe it's widely accepted that tube amps for bass drivers presents lots of less than ideal issues.

To me using solid state across all drivers when biamping will have benefits but if you go to this trouble you might as well go all the way with tubes.

Panzrwagn

"2) "Passive Bi-amping" is BS. You’re still delivering a full range signal to both the LF and MF/HF passive crossovers, the unused half of the signal is just turned to heat."

This is not true. There is no signal flowing through a circuit at frequencies that are filtered out by a crossover network, subject to the slope of the filter. The crossover network doesn't create an offramp for the filtered frequencies to be converted to heat.