It is going to give you a flat level bass response regradless. However, in doing so it is possible that it will not do it in the most efficient way possible. It's up to you how much that is worth for you. You could get 1 SMS-1, configure it, and then unplug subs sequentally and retest the room frequency response to see how well it did its job. If it did it well, no worries, if not, you could get another one or a differeint equalizer.

It struck me that the main point of the SMS-1 was more convenience rather than advanced functionality. I havn't checked around, but your can probobly get cheaper equalizers that do the same thing but require run your own frequency response curve with your own spl meter.