ihifi(John) yes we need more John's in this thread.
I was trying to communicate the idea in a less technical manner when I said "Regarding output, one way to look at it is that the EP600 is twice as loud etc...." but Mojo is right about "perception" of loudness as being different that an SPL doubling.
That Harman article is a terrific article on the benefits of multiple subwoofers.
A pair of 400s as an alternative to a 600 will be a neat comparison. Stacking the 400s gives you the output of the 600 because of coupling. You have the flexibility of separating them for smoother in room response but then have only half the output with less extension than the 600. One other interesting attribute though is the flexibility to set the 400s as stereo subs with monitors or the smaller Axiom speakers.
I'm really looking forward to listening to them hopefully next week. I'm heading up to Dwight this weekend to spend a couple of days on the lake.
