I have used electronic crossovers on and off for almost 40 years, but I just recently tumbled to the realization that there is no one correct X/O frequency for the SW/Main transition, even for a particular audio system. It depends on the music you are playing. Therefore, whatever brand of X/O you select, make sure it is one that has the frequency easily changed by a knob. Units that determine the frequency by means of a plug-in module are simple and reliable, but constrain what you can get out of your system.
