Outboard crossover? Why not?

Active x-overs certainly offer theoretical advantages and (generally speaking) I'm a big believer.  Digital, active x-overs offer even more theoretical advantages and (generally speaking) I'm an even bigger believer.

All passive x-overs (internal or external) present certain issues that demand trade-offs.  Hence the great debate about low order vs high order x-overs.  An active, digital x-over doesn't demand the compromise.  Although (obviously) many here find digital sources (or ADC) a compromise in, and of, itself.  Be that as it may...

My main system is now fed almost exclusively digital program material that's crossed in the digital domain.  There are too many variables at play to say that the x-over scheme is the reason that I prefer the results to any of the many analog based (program material and crossovers) systems I've used in the past, but I prefer the results.

As an aside, several systems use active external x-overs (models from Linkwitz and Salk) come quickly to mind.  Going all the way back to the 80s or early 90s, I think Hales had an external passive x-over option available.

Overall, I find Erik's comments to be right on.  I did not see an easy answer to Inna's question of the difference between an active vs electronic vs passive. could be helpful to others... So,  when a signal from your source comes from your amplifier,  all frequencies hit your speaker.... for now, lets just say 20 to 20,000 hz.  A passive crossover is a filter network... One filter will block low frequencies to a tweeter, another filter will block upper and lower frequencies so a midrange will only see the frequencies meant for the middle region and a low pass then blocks high frequencies and allows the low frequencies or bass only to go to the woofer. 
On an active crossover,  the Filter is put in Front of the amplifier... so you typically need more than one amp.  The filter blocks the signal before the amp,  so 1 amp will be fed only high frequencies, so that amp will be used to play a tweeter... on a 2 way speaker, another amp would only be sent mid and lower frequencies which would go to the woofer.  So on an active crossover,  the dividing network is in front of the amp,  the amp channel plays highs mids or lows and you need 4 channels for a 2 way or 6 channels for a 3 way.  I hope this helps... Erik mentioned a lot of the advantages of an external crossover... I really like having the room to lay out coils to keep electromagnetic field to a minimum.  You can hear it. Erik and Bombaywalla both mentioned the advantages of a digital filter in front of the amps with variable slopes.... There is no substitute here.  Electronic/active crossovers sound better, period.

 We discuss just about passive Crossovers, Inna get question about this,
Active crossover totally different story , The assume amplification  with
different amplifiers and normally working outboard  

Tim, thank you, I have a general understanding of the differences.
We can and perhaps should expand the thread to cover active crossover too, and various implementations. Why not? I think, it will be interesting to many readers.
One thing appears to be very clear - external crossover, either passive or active, has only advantages. I always suspected that.

At the risk of annoying purists....

I'm running a Behringer active xover, but I play about with diy speakers and odd 'hybrid' mixes...albeit not in the 'audiophile sphere' of units available and/or favored.  It does allow a wide range of types, slopes, and points that, with active eq and a calibrated mic on an RTA allows me to amuse myself.  And bi- or tri-amping is another factor in the mix as well.  But one's amusement can be another's horror, so to each his/her own....

Ultimately, let your ears be your guide and let the rest follow....;)