I've seen Twin Turbos, I've seen turbos WITH the stock blower on before, and i've seen twin turbos, a supercharger AND nitrous before.
...but i've never seen 2 superchargers. At least in the other set ups usually the supercharger helps spool the turbos so its making good power down low and up top. Not sure why someone would spend money buying a blower, only to put a 2nd on the car. Seems inefficient to me.