I seriously doubt that dyno is for power at the wheels. If it was, taking account 15% losses, it means that engine is making over 400bhp and 850NM.
Where do you get 15% loss from? BMW are usually quite conservative on quoted power so a figure closer to 400 bhp for an engine quoted at 381 bhp would not be unreasonable. Look at the dyno figures for the new N20 engine conservatively rated at 242 bhp.