Well Lee, keep your 501's or get a fancy digital do everything active crossover setup.
You can play control room any time you want and all changes are reversible.

John, As far as your first link goes,
The way marketers interpret things are often different than what the engineers tell them.
You see in the diagram that I purposely separated the woofer section to show
that its only a separate zobel circuit for the 411 woofer. It does not have to be used
and it has no effect on the horn circuit at all. The 30904 just has 2 circuits on 1 board as shown
in the picture. You have the 30923. The horn circuit is identical. A separate Zobel circuit
can be calculated for any other woofer and does not have to be on the same board with anything else.
A zobel is just another general 6db attempt to control the rising rate of impedance in a woofer.
Hope this helps............