Intercoolers plumbed in series... interesting, I'd have thought they'd be plumbed in parallel.
It's not quite clear in that diagram, but all the properly ducted intercoolers (and radiators, oil coolers, etc) I've seen in production Audi's, Porsche's, etc have the inlet to the duct only 1/3rd to 1/2 the size of the core itself so the airflow slows through the core (more time for heat transfer to occur? lower pressure/temperature?) then the exit duct rapidly narrows to 1/3rd or 1/2 the size of the core to speed airflow before it exits the vehicle.