Maybe this might help you make sense of the responses so far.
Bi-amping a speaker means using two amps to drive that speaker - this you already know.
There are two things to consider with bi-amping:
- the power delivered to the speakers, and
- what's happening with the speaker's crossover - the electronic components inside the speaker that direct only lower frequency sounds to the woofer and only higher frequency sounds to the tweeter.
If you bi-amp a speaker, then #1 will increase: you will be delivering more power to the speaker because you're delivering the combined power of both amps to it.
However, #2 will not be changed: the same set of electronic components - the crossover - will still be doing the job of filtering the sound so that the woofer gets only the lower frequencies of what the amp is feeding the speaker, and the tweeter gets only the higher frequencies.
I am simplifying things a bit, but the point here is that the crossover has an impact on the sound of the speaker. At the most basic level, the crossover has a positive impact because it prevents the woofer from trying to reproduce frequencies higher than it can properly reproduce, and it prevents the tweeter from trying to reproduce frequencies lower than it can properly reproduce (and from destroying itself in the process). But beyond that basic, beneficial role, the crossover also has a somewhat negative impact, because the filtering it does to limit the frequencies that get sent to each speaker driver also has other impacts on the sound of the speaker.
This is just one of the unavoidable tradeoffs that one has to deal with in a conventional, passive speaker. (It's called a passive speaker because the crossover is passive - the crossover comes after the amplification in the signal chain and just filters the full-range amplified signal coming in to the speaker).
So... when you bi-amp a speaker, you are not changing the speaker's fundamental sonic profile, and you are not overcoming the problems created by the crossover inside the speaker. All you're doing is pumping more power into the speaker.
And if your speakers are getting enough power from a single amp, then there is literally no need for - and no benefit from - giving them more power with two amps.
This is why folks are telling you that "vertically bi-amping" some of your speakers is not going to do anything.
Now, there
is something called
active bi-amping, which
@Chrispy has mentioned in a comment earlier in this thread. With active bi-amping, you disable or remove the speaker's internal crossover, so that when you hook up two amps to the speaker, one amp's output goes directly to the woofer and the other one goes directly to the tweeter. But when you do this, you need what's called an active crossover: you need to replace the speaker's original crossover with a crossover that comes
before the amplifiers in the signal chain, so that the amp feeding the woofer is only outputting lower frequencies and the amp feeding the tweeter is only outputting higher frequencies. If you just feed each amp's full-range output directly into each driver in the speaker, then sound will be awful at best - and at worst you'll damage or destroy the tweeter and maybe also the woofer. An active crossover can be beneficial because doing that frequency filtering before the amps instead of after the amps in the signal chain enables you to do it in a way that can minimize negative impacts on the signal and give you more precise (and adjustable) control over how loud each speaker drive plays relative to the other one, and what the exact crossover frequency between the two is.
But most speakers do
not deactivate their crossovers when you bi-amp them. So you cannot actively bi-amp them with a new crossover before the amps. You are only passively bi-amping them, which is what I've described above: same exact speaker, same internal crossover in the speaker, just pumping more power into them - more power that you don't need and that won't make the speaker sound any better.
Does this help at all?