In my older Onkyo (from when they still used Audyssey) it's called double bass and the manual doesn't mention anything about limiting the sub with a fixed low pass filter and there's no adjustment for a low pass otherwise (unless you're thinking about the LPF for the LFE channel?). Just says it sends the L/R/C bass to the sub as well when using the speakers full band.
Looking at James_Ngo's Pioneer manual the extra bass feature is apparently called "Plus" (pg 49-50), don't see a separate LPF of LFE, and a footnote about using the crossover setting says this:
This setting decides the cutoff between bass sounds playing back from the speakers selected as LARGE, or the subwoofer, and bass sounds playing back from those selected as SMALL. It also decides where the cutoff will be for bass sounds in the LFE channel.
Bad enough some sub manufacturers misuse the term crossover....