That sounds like a rather unique solution: 3 high on each side! One of many possible solutions, as the next post by @mrdecibel went from 2 subs to 1.
It's great to hear the variety of approaches hear to 2 channel music. I think I'm going to go with 4 dual opposed subwoofers, with the first 2 placed in a slightly staggered fashion just to the inside of the left and right speakers.