Norwegian OM606 build
Norwegian OM606 build
That sounds real interesting. I have yet to actually see a 3-stage turbo setup - most people, and companies, end up using at most 3 turbos in a two-stage setup. BMW with their two high-pressure turbos that gate in and out for better response.. and drag racers/sled pullers with two low-pressure turbos for massive amounts of air.
Depending on how small the high-pressure turbo has to be, you might have to use a wastegate+bypass air valve to bypass it at higher RPMs.