In his great Tech Talk Tuesday videos (viewable on You Tube), GR Research's Danny Richie describes and explains how he uses discrete parts in the x/o of loudspeakers to provide compensation filters for addressing driver ills. Part of that explanation is why an outboard electronic crossover, while very useful for some applications, can provide only "textbook" filters, NOT compensation filters for drivers needing help.
Great stuff, everyone should watch them all.