Passive biamplification questions

I want to know your opinion about the use of two stereo amplifiers in vertical passive biamplification.
My speakers have biwirable or biamp. connectors and my preamplifier has two main outputs, so I can go to passive biamplification without problem.
The passive biamplification really represent an upgrade ?
If the answer is yes: Why it is too difficult to find system that use it ?
Please let me know your experience and opinions.
You're still sending full range signal to woofer and tweeter. Better to crossover Actively with an inexpensive Behringer, or better yet a Rane. More work but an order of magnitude in improvement.
I can only speak from a single set of listening sessions, using Linn gear. I was able to compare three setups: passive biamping using basic-level amps (LK85s), single-amping with a better amp ( LK140), and active biamping using basic amps.

In a nutshell, the three setups came away in the same order. The better single-amp system beat the passive biamp system. The active system came out on top but not by a whole lot. The quality of the amplification was a key factor, so I deduce that a great stereo amp beats out two ordinary ones.

From my experience with these three setups, then, I would say skip passive biamping, get the best single amp you can and when you can afford it, go active with a second high-quality amp.
You should contact the manufacturer to see if there are any potential problems with bi-amping. Some amplifiers go into oscillation with some speakers in biamp mode.

You didn't say if you were using identical amps.

Using identical amps vertically will not increase perceivable power much since most of the the power is used by the woofers. However, the drivers can interact with the amp and with each other. Biamping reduces that interaction. For twice the amps, don't expect twice as good.

Different types and models of amps have various strengths and weaknesses. For example, I enjoyed the Monarchy SE100 for mids, highs and imaging but they lacked bass. My previous amp lacked detail but was only a little shy of a nuclear bomb on dynamics. Biamping those together, I got the "best" of both worlds, eventually. Unfortunately, those amps did not have the same sensitivity or gain and it wasn't a happy marriage without some electronic counselling.

An attenuator on the louder amp is DIY project beyond many. Using an active X-over along with passive X-over in speaker is possible but tricky. Removing the speaker's passive X-over and replacing it with an active risks turning the speakers into junk or can have fantastic results. There are a couple digital X-over/ preamps available that can do everything except grate cheese.

All this is based on a low crossover point (80 to 120 Hz). Above that will get into critical midbass where subtleties aren't so subtle.
If one is using two class AB or A/AB amps the more efficient drivers which are usually the higher frequency drivers which our ears are more sensitive to may have more class A amplification available to them which may sound better. IMHO more often than not and the specific cross-overs may have a lot to do with this, using identical amps is prefered.