Reading the evils of crossover thread is interesting.
With help, I put together a Dayton Audio 8" full range driver in a U frame, with 3x8" servo subs. Listening to the system without any correction for the full range driver was pretty bad. Using the MS-3 and dspMusik crossover, I did simple corrections to flatten the response of the full range, and measure to integrate it with the servo subs.
If anyone tells me it sounds better before the crossover, I would show the them difference. Not even close, and sounds much better corrected.