Thanks for the compliments Alan. They do sound great, as I'm certain yours do too. I think it is safe to say that many of us would give anything to be in your place; highly respected in your field, and working for none other than our favorite audio company.
As stated earlier, my reasoning for getting dual subs was for bass uniformity in the room, and I initially had one in the front and one in the back of the room.
But now that I have them both up front (based upon my in room tests with the SMS-1), there really isn't much difference between running one or two. In my current placement arrangement, I find that I'm getting about 4dB of additional headroom. This is only a benefit at the extreme loud points in most soundtracks. With the levels properly calibrated, 99% of the time I am hearing the same as if I was running with one sub.
However, with 2 subs there is more driver area- which do provide a larger "sense" of realism by moving more air during the high impact scenes or explosions. I would guess that this plays a big part in why sub enthusiasts prefer more subs/larger drivers.
Is it worth it for 4 dB? It totally depends on the person, and is subjective. There are some here with 4 subs, even 600s.
Do the dual subs look cool up front?
AFL!!!I wonder if Mark is getting his AFL phrase trade-marked so I can pay him $1 every time I use it? If I keep it up, I'll need to send him one of the 500s as payment 
