The Apollo has landed!
After much deliberation, I decided to order a Westcott Apollo 28" Speedlight Set from B&H. James was ordering a number of stuff from there... so I tagged along on his order, and he also ordered one for himself.
At US$119.95 + shipping, this does not come cheap. The speedlight set comes with a hotshoe umbrella adaptor. It has the same internal concept as the umbrella softbox, but the advantage is not only the size, but it has a recessed front to control the spread of the light.
I shot a few shots at a low 1/128 power on the Nikon SB-80DX, and the light that came out was even throughout the white area. Comparing to the umbrella softbox, the Apollo gives a more even distribution of light. This is likely because of the larger volume interally where the speedlight can be placed further from the silver reflective area, and also a larger area for light to bounce internally.
I particularly like the design where there is a cross zipper area to accomodate for the lightstand to go through into the softbox. The volume inside the softbox is large enough to contain a monobloc light.
Here are 2 pictures of the Apollo Speedlight Set, the first showing the internal construction and how the speedlight is mounted, and the second is the external showing the recessed front.