This is for the X6 xDrive50i. The two turbos are used one for each bank of 4 cylinders, ala -35i powered cars. BMW positioned the turbos and the catalytic converters in the valley of the V8. Instead of running the intake manifold to the inside of the V and having the exhaust manifold com out from the side of teh V ans is usually done, the intake comes from the sides, and the exhaust manifold goes to the turbos in the middle. This results in very short intake and exhaust manifold and, thus, reduced turbo lag (basic fluid dynamics -- yes, hot air is a fluid -- shorter manifolds means less pressure drop).
If you think about it, a lot of materials science and characterization research went into coming up with a design with turbos that maintain the intended functionality despite being in the hottest place in the car (not counting the inside of the engine).
Very innovative. Scientific American picked this car among one of the top-ten cars in terms of technological advances.
Oh, and the way the engine is configured... well, it fits in smaller places than one would expect for a 400 hp, 450 lb-ft powerplant
The subject in teh flesh: