I am picturing 2 desk fans pointed at each other and what would happen is that the air will move out perpendicular and radially to the normal flow of a fan. Now if the box is the plenum and the fans are cut into it you are basically describing a twin turbo setup. The problem here is that you don't have 2 fans you have a fan and a pump, both of which have different characteristics. So now that you are not dealing with the MAF issue and it's SD. So how do you control the valve that keeps the supercharger from blowing air back through the turbocharger? You are going to have to dump the turbo air to atmosphere in order to get it to spool. A deadheaded turbo will not build pressure because it cannot gain speed, it doesn't matter that there is more exhaust production or not it will only spin so fast and depending on the boost from the supercharger and the size of the valve the amount of pressure is going to be very high, way higher than the boost pressure. If you had 15 psi out of the supercharger with a valve that had 2 square inches area on it the pressure is going to be 30 psi so then you need to have a 2 way valve that is controlled by some other function so that it vents the turbo and allows it to spool then closes and routes it into the manifold. But then again if the turbo is making more boost then it starts making the supercharger harder to turn.
