Give it a few taps with a ball peen hammer while you're turning it, lightly. Allen keys are terrible, which is why BMW uses torx everywhere, but a copper-gasketed steel plug in an aluminum oil pan is going to bind up no matter what you torque it to, correct or not.
Took 8.75l for mine, and about 45 minutes start to finish. Took another 10 minutes to let it idle long enough to get a few accurate readings and re-readings. I started at 8.25l, warmed up and checked, and it was calling for an additional 3/4l. Added half a liter and everything's peachy. Driven it fo several days now and it hasn't budged. Doesn't seem like such a big deal to get right the first time if you're patient?