so how does the stock supra regulate boost to the engine? Is it through a flapper gate system like on the RX-7?

Sorry I just thought that on the MKIV that both turbines were exactly the same size and fed 3 cyls each with the same boost.. thus being in sync.. not sequencial.. so at 3K rpm both turbines being exact sizing are at the same rpm producing the same boost, not that one was helping it to 3k-4k and then the other (larger turbine) was taking over...

I figured that they were both the same size and 2 of them because toyota

A: Has a ton of CT's already, didnt have to change much in their ordering cept maybe wheel trims and stuff (not sure on the size of the supra twins compared to the MR2 or something, might be the same i dunno)
B: Twin turbo sounds cooler than a big single (which they coulda gone for a T3-T4 sized turbine stock and gotten the same results... or maybe a T4 of some kind..) Also since the 300ZX was already Twin Turbo (since it has to be) and the skyline as well (prob for cheapness reasons kinda like the supra) were all TT.. having the supra be not Twin Turbo would hurt sales due to less coolness factor.....

I just thought that turbos on the supra were in tandem like on the 300zx / skyline

Not in sequence (1 then 2 after more RPM) like the RX-7 with its flapper gate switchover..