There's a reason the subwoofer is getting tones to 120 Hz when it's set to 60.

60 Hz is the nominal -3 dB point for the filter. The signal to the subwoofer is attenuated by the 990* above this frequency at 24 dB per octave. One octave above 60 Hz is 120 Hz, so the signal will be reduced in amplitude by 24 dB. This is just over 200:1 power ratio but to our ears it's somewhere around 4:1 or 5:1 perceived amplitude.

* Per the manual, specifications page

It would be nice to have a filter with an infinite slope. However, this is not possible in the real (analog) world. In addition, as the slope gets steeper it becomes much more difficult to avoid ripple in the frequency response and adverse phase effects. Even with digital signal processing there is a practical limit (processing time, delay for # of samples, etc..)