Usually when I tweak crossovers its with an eye to the SMS real time display so I can see its effect on FR. Blending the sub/speakers to achieve flat FR on either side of the crossover point depends on various factors such as slope of the low pass filters , phase, level etc. The conventional wisdom about not having two low pass filters in tandem is that it plays havoc with phase at the crossover point and can cause irregularities in FR at and near the crossover frequency. Having a brickwall filter like we have in the EP subs also means a discontinuity in sub's response above the crossover point compared to the more typical 24db sloping Linkwitz-Riley 4th Order low pass filters you find in most other subs.
That brickwall filter works well if the sub is level matched to the speakers, you are not running the sub hot and if the speakers have flat FR. Room acoustics not withstanding. As we all know Axiom speakers are engineered to linear FR. However most people (not me) like running their subs 3-5db hot so that alone will mean a discontinuity in FR at the crossover point because of the DSP brickwall low pass. Also depending on the processor filter it may or may not introduce phase anomolies or possibly intermodulation distortion.
Perhaps there is something about the DSP chip that avoids the usual problems with using two low pass filters? Conceptually I can see why it could work but only when the sub and linear speakers are level matched and the processor low pass filter doesn't cause phase problems. Anyway, I'm looking forward to some clarification on this one.
