To go twin charged and make it efficient, I would have to say you really need to take the M90 to it's limits first. Then I think zzp says a minimum of a 67mm turbo is needed when going twin charged. The benefits of twin charged would be no turbo lag, as the m90 is used and then after the turbo spools up, electronics will open the supercharger bypass. You would need a intercooler below the supercharger as the M90 is still producing hot air.
I would stay away from cartuning as they are not experienced in this area and I think special exhaust work is needed.
You would probably need #60 inj., unique pcm work done, stg 2-3 intercooler setup, front and rear powerlogs, stattama turbo crossover t4, a bigass turbo, a air/air intercooler, a cam, and a lot of extras.
And a transmission with $800 1" chain, probably $3500+ tranny rebuild altogether.
