Not Duke, but some people put a "budget" active electronic crossover into their system, and find it to reduce the system's transparency. Lots of people are even using those cheap digital x/o's. Oy! They contain Opamps, IC's and other sound-compromising parts. Plus, who wants to digitize an analog signal?!
There are some real good x/o's available, at varying price points. Marchand's tube x/o's are popular with DIYers, and the First Watt B4 is a real nice little unit. It was unfortunately recently discontinued. Nelson Pass makes a great one, but it's not cheap. People like the Bryston, but it's pretty limited in adjustability.