I've used my Anti-Mode with both a single sub and a dual sub setups. On duals you still have to know the basic's on how to set them up (gain/level match, phase, location, location, location
). The Anti-mode works with the summed output of the two subs as a single entity, but it does do so very well. Mismatched subs may present more of a challenge as the EQ is not differentiating the signal it sends between them, but if they are a matched pair and set up properly you should be fine. Many people have run multiples (including some who run a sub/MBM set up) and reported good results.
REW is Room EQ Wizard, a freeware app that can be downloaded from another forum, just google it and you should be able to find it easily. A BFD is a Behringer Feedback Destroyer, a pro-audio piece of equipment that is frequently utilized for its parametric EQ features and relatively low price. They are plentiful online or through retail stores such as Guitar Center. The same forum that hosts REW has a dedicated section to each of these items, with FAQ's, set up walk throughs and many knowledgeable posters who can assist setting up, running and then understanding the results given by REW.