OMG so many theories that are half baked or half explained in one place it should be made a crime. For the people with the differential/sequential turbo setup idea, think fd rx7(one combined cast manifold feeding the exhaust sides of two different sized turbo's with a valve that switched the flow between the two). For cars like ours a divorced bank system works great for packaging, and lets you put the turbos right next to the manifolds for the most flow and heat retention. I would suspect that the stock manifold is MOSTLY separated but retains an inner passage that links the 2 plenums together molded into the plastic. Think balance tube on a VG engine. It is nowhere near what you need to be able to run two dissimilar turbos, which wouldn't work anyway due to the uneven exhaust backpressure. You could brobably get it to work if you did a single kit and used a mazda style turbo setup but those setups are mostly crap and get changed out for single turbo setups because they aren't very good for high horsepower applications. I vote we let GTM do the thinking.
Edit: Surprised no one has thrown out series twin turbos while you're at it geez we could run like 50psi
