how about just wait for some new technology to filter into the aftermarket manufacturers catalogues...
how about keeping it single turbo but instead of using a normal turbo, why not use a twin scroll turbo???
"what's a twin scroll turbo" you ask? take a look at the replacement for the liberty/legacy B4 twin turbo.... Subaru realised that their twin turbo design on the ej20/25 was flawed.. so they set their geeks about designing a new turbo system that could replace the TT setup they had....
well, that's what the subaru tech guy told me at the sydney motor show/subaru dealer. The new B4.. or liberty GT as they renamed it uses a twin scroll turbo... basically, 2 turbos in one....
it has 2 impeller blades... with 2 stages of spooling/boosting.... i have no idea on how it works.. but i gather it just has 2 stages controlled by actuators/gates...
im gonna do more research now, hehe...