Hey Rattus,
So, what happened was, I actually didn't realize that there were two lenses, the old f/3.5 ZEN and the newer f/2.8. Just before my trip, I bought the 2.8 and the compact dome port, and didn't have time to try them together before I left. When I got back, S&S basically told me that they weren't supporting the newer lens and that I was out of luck. I originally bought the 14mm only because I wanted something that I was sure was supported so that I didn't have to mess around with figuring out extension rings, etc. Since it didn't work, and I was within the time frame for returns, I sent the lens back for a refund.
Long story short, when I tried to fit the Sigma in the compact dome port, it was maybe 1/2" too short because of the fixed lens hood. You could probably either add an extension ring, or simply use the larger dome port.
I'm going to go a different route personally. I bought a Canon 17-40L lens and will be housing that instead. I've looked into it a little, and with the compact dome port, I think I need a #56111 Intermediate Stiffening Ring 40. The same ring may also work for the Sigma. The zoom gear may be a bit more difficult, but it looks like a zoom gear that fits the 16-35 may work with the 17-40 since they are fairly similar in size / shape.
The unfortunate part is that I haven't been diving much this summer because of my work schedule, so I haven't been super motivated to sort the ports out.
Hope this helps, let me know if you have any additional questions.
Tom