Rob,
According to the answers in
this thread from another forum, the crossover frequency on that Sony is 120Hz.
If you want to use the bass management in your Sony and set the speakers to "small", then I suggest that you either use the LFE input on the sub or use the line-level inputs and set the crossover on the sub to the highest value.
EDIT: The VX-10 brochure mentions an LFE input, but the owner's manual doesn't show one. So, you might not have an LFE input (which is the same as the line-level inputs except that it bypasses the crossover in the sub).