Biamping (or tri or even quad-amping in the concert scene) is the only way to go if you need to get stupid loud (> 140 dB). It is better for normal use too, you just don't get the cost advantages (It's a lot easier to find a 100 W amp with a great extended response than it is to find a 10,000 W amp with simular specs).
There is some risk that you will toast your tweeters if you don't get things setup right or if the crossover frequency gets changed by accident (good reason to not make the crossover frequency too easily adjustable).
It's generally a good idea to leave a cap in series with your tweeters even if you use active crossovers. Just select a cap that will crossover the tweeter an octive lower than normally. This shouldn't have any negative effect on the sound quality and will hopefully save your tweeters from catching fire if somebody (who me?) hooks things up wrong.
bi, tri, and quad amping is popular even if you don't need very high volumes. Certain amps match up better with certain drivers (i.e: some like tubes for the tweets, and SS for the bass), and you'll generally have a much lower distortion, and infinite flexibility in the configuration of your speakers. Many people have adopted fully active speaker systems now, and for several good reasons.
IMO, there are very few disadvantages if using a high quality active x-over, such as that from Marchand.
(BTW, I currently bi-amp, and will likely move to tri-amping when building my next set of speakers)
Don't disagree, Bi and Triamping is superior to passive crossovers any way you want to measure it. The possibility of roasting drivers is something that everyone who used active crossovers needs to keep clear though.
I have a live sound rig that uses active crossovers and I use Speakon connectors (NL4) so I can make both the high and low band connection with a single cable. Which means I can't get them swapped at the amp or speaker end. This doesn't stop me from swapping the inputs to the amps wrong, but that's another story (color coded heat shrink on the cables, just be consistant and burn it into your head: Red is low frequency, Blue is high frequency, just like light).
There is a diminishing rate of return as the number of active XO points increase. The primary sonic benefit is obtained with bi-amping, as a result of the removal of the large inductors in the woofer XO. These have a profound negative impact on the amplifiers damping factor.
Marchand are indeed good active XOs, but like all generic actives they lack baffle step compensation.
If a person is adept at engineering and building custom electronics, then baffle step or any other form of EQ can readily be incorporated in the circuitry. The only down side to this is that any change in drivers usually necessitates and complete redo of the custom circuits
Thank you all for your input.
The main point that I want to look at is linked to damping, (thanks ThomasW) and cost.
It is my belief that the biggest problem with passive crossovers, even those with expensive caps and silver coils is that the amp's control of the driver goes out the window at the crossover point! Both the inductors in the woofer cct. and the caps in the the tweeter cct. (lets keep it simple, 2 way system) decouple the drivers from the amplifiers at the critical crossover piont (loss of dampening). Check Qes and Qms, speakers are mainly controlled electrically, (and this is the way it should be). I suspect that is why many high end manufactures stick to first order crossovers, (as well as other advantages). In fact the dampening is compromised through out the drivers range.
How can multi amping be cheaper? I can brew good quality 100w amps for $100 Aust. each. I feel that directly connecting a low impedance amplifier to each driver will get me better control of the speaker than buying expensive drives and feeding them through passive crossover.
I'm betting that a $200 woofer direct amped will sound tighter than a $1500 woofer fed through a passive xo.
Some people pay a fortune for low impedance speaher cables, if they only knew what their crossover was doing to their amp-speaker connection.
I have never toasted a tweeter but I have replaced many in other peoples systems, (including active systems) but thanks for the warning.
Your thoughts gentlepersons?