Thanks. Nice setup. Here's how I accomplish pretty much the same thing.
http://www.pbase.com/rloeb/image/47810762
The bracket is part of a Wimberley, connected to an L-bracket that's always on the camera. The top plate is from RRS. As you can see, there's a Quantum Turbo underneath, and it powers both flashes (using a Y-cable). What you can't see is the little piece of fiber optic that is stuck into the side of the leftmost (from the front) SB-800, which is the master, and delivers the preflashes to the sensor on the side of the other flash, which is driven as a slave. I drilled a tiny hole into the left front side of the SB-800 and inserted a very small piece of fiber optic (obtained by stripping an excess piece of audio fiber). In general, the slave will fire if there's any light reflected around the room, particularly if there's an umbrella in front of the mess, but the fiber optic makes it work outside at night, etc.
When I use this with an umbrella, I turn the heads around but leave the bases as they are; I also raise the whole unit up by adding a Wimberley extension leg. A standard umbrella bracket mounts to a 1/4-20 stud in the horizontal bracket. I still poke myself in the eye, so I usually prefer to put small softboxes -- or Gary Fong's Lightspheres -- over both units. It's a lot easier to manage and I prefer the quality of the light.
Incidentally, with a larger softbox I just hook two SB-800s together, top-to-top, with some velcro and put a large rubber band around them. One of the SB-800s is reversed, so the sensors both point in the same direction, and the one on the bottom goes into the shoe mount for the softbox speed ring.
Rog