Here's the general idea of the twin-charger kit.
Right now we have a supercharger. Great for getting boost right from the get go, but eventually as you go to higher and higher boost levels you have diminishing return. With a turbocharger, it's easy to get high boost at high RPM, but it takes a while for that boost to build (known as turbo lag). Well, if you have both a turbocharger and a supercharger, you can have some boost right when you hit the gas and until the turbo spools up, and after that, you can have a LOT of boost from the turbo. Essentially it is the best of both worlds.
That being said, i have a question for those that know more about the M62 than me. The M62 has a bypass valve that can open and let air into the intake without going through the supercharger, correct? Now, i'm assuming that the bypass valve is also used to keep the boost below 12psi? I'm guessing it works like a wastegate and actually recirculates the extra boost back into the intake pre-supercharger. If that is the case, then shouldn't the bypass valve start opening at 12 PSI, and, if the turbo is spooled, shouldn't that valve actually let more boost in, without going through the supercharger? If so, that valve is really awesome, as some people (i think) were talking about the air having to go through the supercharger even after the turbo was spooled. With the bypass valve (if it works like i think it does) it don't have to!