Well first off, you should just go to a good bootfitter. I agree, the Soma-Tec seems like a pretty good idea, however I haven't tried it personally and I imagine it's going to fit/work differently for different people depending on their foot shape, natural stance, etc. If you want some info from someone who has been riding them, try PMing heff, he should be able to give you some input.
Nordica and Fischer do their "duck Footing" differently. Nordica's is less drastic and is abducted from the heel. The SOMA boots are more drasticd and they are abducted from the center of the foot, so the heel is turned in a bit and the forefoot is turned out a bit.
advantage to both of them is that they allow you to ski in a more natural position. Think about when you're just standing around naturally, your always gonna be abducted. So, to take that to a ski boot is very smart. Basically, you're gonna be able to roll over to your edges much easier and be more comfortable in doing so. Hope this helps
Another difference is that Fischer has different degrees of abduction depending on what boot you are in. The higher end models have more than the lower end. Nordica only has it in their Sportmachine lasts, which are kind of low end boots. They used to put in their race boots, but stopped. We do it in our Hawx (100mm) & Live Fit boots (102-6mm), but not in our Race, Burner, Tracker, or Volt concepts.
As said before, go see a boot-fitter to see if it's something that works for you.