All of your current examples, are not quite accurate.
I have been able, to have, a sub, run by a separate amp, that
has been tweaked, to emulate a first order crossover,
while maintaining, time and phase, coherency, of the complete
speaker system!
I have been able, to have, a sub, run by a separate amp, that
has been tweaked, to emulate a first order crossover,
while maintaining, time and phase, coherency, of the complete
speaker system!