I agree that this makes no sense, but when you build a 2.5 way stereo crossover for just over $100, sometimes shortcuts are taken. Elsewhere in the above referenced thread, someone says he measured one and that is how it behaves. It is cheaper to add one variable low pass after a summing circuit than it is to add a pair of high pass filters and a summer and a low pass filter, with all the frequencies coupled.
I don't have one, so I can't be certain by measuring, but that is what the consensus in that thread says.
Marc
But it does work like that. its now collecting dust somewhere in an old rack.
I used to use the passive crossovers in the top boxes so I just used the high outputs of the behringer to drive those and either the Low or Sub output to drive the sub(s).
All EQ's we had had an 12dB/Oct. HPF at a freq low enough to be used for subwoofer "protection".