I always understood that the rationale behind using dedicated subwoofer EQ tools (SMS-1, AS-EQ1, RDES, etc.) prior to using overall room correction tools like Audyssey was that it was the only practical way to merge the two forms of EQ. The dedicated tools frequently had more available bands of EQ available specifically for the sub and could do a better job of getting subwoofer response flat, then the room correction addressed the full-range speakers and did whatever it could with the subwoofer. (In early room correction and even some current models, their sub EQ was of limited capability, which just reinforced this idea.) The SMS-1 is the only such sub EQ I've used, and while it has multiple sub outputs it operates with a mono output and applies the same EQ to all of the subs.