Currently using a crown XLS bridge mono w/ lowpass filter @88hz (sounds OK this way) for a B460 sub 2245H. Mains are L300's cut at 50hz using another crown xls (well today anyway )

I do have a BX63 and always used it, but I don't need to pass the mains thru it in order to remove low frequency to the mains, and so the only feature I was interested in was the 25hz/6db or so boost. It seemed when I have the BX63 in use, (with whatever amp used actually), I could not hear this boost, or I suppose its ability to keep it flat down to 25hz.

I have moved the BX63 in and out with the crown, but I can't hear the difference. The electrolytics inside have been replaced, and seems to function normally.

Maybe the need to have a BX63 is room dependent, placement, etc., My room is small but has lots of treatment for bass in corners. The system is not used for HT, only music.