I have 2) SB4000’s paired with Wilson Tune-Tots. I have the SVS output levels set at -3, but the whole system is controlled by a XTA DSP unit, using Audiocore software installed on a laptop. Crossover points and volume levels will vary somewhat depending on the recording but with most recordings the low pass is set at 173 Hz and the high pass at 177Hz with the sub output level set at +2.5 dbu and main output set at + 8 dbu.
I also have 2) non SVS subs being used as satellite subs with their output level usually set at + 1.5 dbu and their low pass filter set at 78 Hz.