well, from looking at the maintenance diagrams for the N54 it looks like the front and rear 3-cylinder “groups” each exhaust to a seperate turbo. Presumably the firing order is designed so that each turbo gets a constant-ish stream of exhaust. Both turbos compress into the same pipe+intercooler+intake system (although really only the large one needs it). The front turbo is smaller, and spins up faster, so you get coverage over more of the rpm range.

Contrast that with the V-engine twin turbos, where each bank blows one turbo and gets intake from that one turbo (generally). Or, porsche’s design where each bank blows a turbo, but one turbo compresses air through the intercooler to the other turbo and then into both banks. Lotus’ twin-turbo V8 uses seperate turbos per bank but changes the usual firing order (and crank design) to get consistent exhaust over each turbo at the expense of engine smoothness.

Anyway, what I’m getting that is that since they haven’t proposed a quad-turbo for the inline-6, nor a tri-turbo for I6 or I4, that there may be a special design that works well where you have 1 turbo per cylinder. Considering the exhaust flow, manifold routing and other issues, I’m speculating that they’re using the exhaust pulse to their advantage somehow, rather than averaging out like in other designs.

Puuuure speculation though