I take it that your mains (the combination of Sunfire subs and VMPS RM/X's) are being run large. This means that the Servo 15 will only be active for the .1 LFE track and for low frequency data crossed over from other speakers (assuming that your processor steers the data to the sub and not the mains), which is fine but poses one problem: setup. The easiest way to do that is to temporarily set the mains to "small" with a crossover of at least 80Hz (you might even bump the crossover to its highest setting, since your sub will see some LFE channel data above 80Hz) for the purpose of dialing in the Servo 15. If your processor supports bass management of the multichannel analog input, you could also connect the SMS-1's EQ outputs to the left and right surrounds of the multichannel analog input and see what it does, but I'd personally prefer to just set the mains to small temporarily. Turning off the subs wouldn't help any, because what you need is to make sure your receiver or processor is applying bass management to the left and right channel inputs. Once you've got your mains set to small, set the SMS-1's input to stereo (no surround processing or analog bypass), get the receiver volume adjusted so the mains are playing at around 80dB, and adjust the SMS-1's volume so that the Servo 15 is doing about the same. Then tweak EQ's to your heart's content.

If you haven't done so already, I'd also recommend disabling the SMS-1's low-pass crossover (highlight the "SETUP" entry for the "Low Pass Xover Freq" on the System Setup screen, press "Select", press "Reset", and press "Select" again to turn the low pass off).