Replying to my own question, I looked more closely at the manual and it gives the answer.

Re: the 60/80/100/BP switch, when you pick one of the numbers:

This switch lets you adjust the internal
crossover (bass management system) to route
user-selected low frequencies to the
subwoofer output (R25) while the rest of the
audio signal is sent to the amplifier and then to
the main loudspeakers.

If you pick BP then it sends the full spectrum signal to the sub AND the speakers as well.