First, what position do you have the volume knob on your sub? If it is at or past twelve o'clock, you may not need a lot at the SMS-1.

Second, when you have the volume at 5 did you get a smooth curve from low frequency to up past where your fronts took over? If so, moving it up to 10 will create a line that slopes down to a level a few dB lower when you transition to the front speakers. That may be an effect you prefer, but it is not as "ideal" a configuration as calibrating for a linear response all the way up to 200Hz.