The question which all the (well meaning ) previous posters are missing is what to set the sub at. The answer is to set the sub at the highest crossover you're using, in this case 100 Hz. In my case (since I cross my QS4s at 120 Hz), the answer is 120 Hz. My VP100 is crossed at 100 Hz, and the 50s are crossed at 60 Hz or 80 Hz, depending on the source.

I am the Doctor, and THIS... is my SPOON!