Here's pics of the twin charged 2.4 on Jbody.org. It's a pretty sick setup:
Although twin charging can be done with some success, I'd much rather use just a turbo. It's a common myth that turbos always have all kinds of lag. When you properly match the size of the turbo to your engine, there will be almost no lag and you'll still have more power potential than you need, especially when using a ball bearing turbo. It's when you start matching 800hp turbos to 1.8L engines that you'll see a lot of lag.
Twin turbo and Bi turbo are the same thing, where two of the same size turbos are used and each one gets its own bank of cylinders to feed it. Sequential twin turbo is when a small turbo is used to spool a large turbo. Sometimes they will each have their own bank of cylinders, sometimes the exhaust will run through the small one and then through the large one. The most complicated version is when exhaust is routed through the small turbo and then at a certain boost pressure a valve opens and allows exhaust to flow to the large turbo, even though they're both mated to the same exhaust manifold.
His original car (blue Sunfire) made 240whp on 7psi twin charged, then his new car (silver Sunfire) with a different engine made 248whp at 11psi with the same twin charged setup that he swapped over. Those pics up top are of his new setup on a fully built engine.
I'm not sure I agree with you that twin charging is more efficient, but it's certainly a way to get good response from a big, laggy turbo. Like you mentioned, this setup would be most efficient if the supercharger could be completely bypassed once the turbo is spooled.