So set the LPF from 40Hz-120Hz?
Learning every day
High pass (ie block everything below this point) at 40
Low pass (block everything above this) ...usually 100hz or so. (no harm to subs if you take this too high but is starts getting in to territory your mains should be doing if you get too high)
This passes everything between 40 and wherever you Low pass at. The high pass blocks the bass below what your sub can handle and the low pass handles the transition between your tops and subs.
These are the lowpass and highpass values for the SUB channel
. In your original post (with the highpass at 100-130 Hz) were you talking about the highpass to the tops? Or the highpass on the subs? The subs need the highpass at 40Hz to prevent over-excursion of the driver. You need 3 filters.