http://sound.westhost.com/biamp-vs-passive.htm

It is very apparent that with a passive crossover, things are not as we would like them to be. Each variant has problems, and as with all things, a passive crossover is a compromise. IMO, this is not a compromise I am willing to make, as the performance is too unpredictable - this explains why so many passive designs require a considerable amount of tweaking before they sound their best - and may still disappoint the listener in critical listening sessions.