Is More Better?

Check out AudioKinesis and the 4 subwoofer swarm ... the extra subs are very much about getting even bass response throughout the room ...and setup is not difficult with 4 subs - a single sub is most difficult to place...

Uhm what will be a better purchase than a subwoofer to combat room mode stacking and helping fill some nulls of the initial sub system?

Cos nothing bought outside of some broadband absorption is going to be more important than bass management via a multi sub system in giving your system a greater sonic benefit and that's physics. Can't run around that with voodoo purchases

It sounds like the "Swarm Technique" where subs are located in non conventual locations in the room. Finding the locations is the trick. Time and patience.

THE CRAWLING AROUND MANEUVER WON'T SUFFICE?

@janewyman, good read see here and here!

Mike