A twin turbo with a sc sounds sexy, but is certainly not needed. The roots or screw sc rips the car until one big turbo spools and takes over. 2 turbos help to spool a little quicker which is not needed with a positive displacement sc for the bottom end.
It is important to realize that you cannot use a centrifugal sc. Go check out roots or screw supercharger torque curves. The boost from the sc and the turbo are not intended to be used together, but first the sc then the turbo. There is no need for the extra weight, money and complexity of a second turbo.