Subwoofer Filter setting... help

I need advice on where to set the cut-off filter on my sub. It has a knob that adjusts the cut-off to 35, 45, 55, 65, 75 or 85Hz. My NAD receiver has a dedicated sub-out that cuts everything above 100Hz. I mainly use it for listening to music.
Given that there's no filter bypass on my sub, my question is this,
Should I:
1. Set the sub as high as possible (85Hz) to minimize double filtering by the receiver and sub, or
2. Set it at the frequency where my speakers drop away (about 55Hz), to prevent overlap and phasing problems?
What is the NAD doing with the non-subwoofer signal? If it is high-passed at the same 100 Hz you wouldn't want to set the subwoofer lower than this or you will get a big dropout between the two frequencies. If there is no high pass filter in the NAD you will need to set the SW low so as to avoid booming bass in the range where both speakers are functioning.

You don't have to use the NAD SW output, since your SW has its own filter.

As with most questions about SW, it's hard to predict what will be best for your particular system, room, type of music, and your ears. Experiment until you find what you like.

In my case, after years of experiments, I concluded that the optimum SW crossover frequency differs a lot depending on the music I am playing, so I had to get a crossover where the frequency is varied as easily as a volume control.