Use a pair of Y cables from the preamp to split off the L/R signals for the SMS-1. (I cannot remember if one can use the SMS-1 to do this but that might be possible.) There is a small delay introduced by the SMS-1 but that is folded in with the rest of the adjustment you will do to integrate the subs with the main speakers. However, you should also use the SMS-1 display to assist you in placing the subs as optimally as possible before invoking the EQ.
Frankly, I would prefer real bass management with delay/level/crossover including a HP filter for the main speakers but that does not seem to be where you are going.
Frankly, I would prefer real bass management with delay/level/crossover including a HP filter for the main speakers but that does not seem to be where you are going.