We have tested the Geddes approach too, it definitely works. Compared to the JBL/Harmon is treats each sub woofer as it's own unique "contributor" to the total node cancelling effect and tends to have more complex and extreme EQ curves, but it really works- Geddes is quite an amazing engineer.

When you have spent your life hearing music in rooms with modal issues these multiple sub-woofer solutions are pretty mind blowing. Bass sounds even over a very large area, the clarity of bass notes is striking, the decays are tight and you can hear down lower then you would ever expect in such small rooms. Another strange side effect is that the imaging in the midrange and highs is dramatically improved

This is really quite a big deal, glad it's getting discussed here