And again - you are missing the point of the question. Do try to keep up.
The BU-1/is a powered sub WITH its own crossover.
The Bryston has two (2) sets of amplifier outputs.
My signal path has external signal processors between the Bryston AND the Hafler
i DONT NEED an extraneous high-pass filter between the subwoofer AND the Hafler.
The home theatre people AND stereo shops here in Portland have given me mixed msgs on whether i lose ANYTHING by running with just the hafler in my signal path (and using the signal processors throughout) OR running the subwoofer off the 2nd amplifier outputs (with an RCA Y-cinnecror) for each channel to feed the subwoofers, but removing the signal processing, effectively, from the subwoofers.
And for the record: everyone says you dont need/want to use an additional filter for the subwoofer. It is like taking a vitamin when you dont need to.
Sorry for getting testy, but i thought this is a fairly straight forward RFC.