1 litre pr 1000km is as somebody mentioned correct according to the manual. This is clealry just to prevent people from complaining on high usage..
I would say that any Petrol car using that amount of oil has a serious failure. Unless you hit the rev limiter 10 times a day, then it will spit oil up the breather system.
I've driven my S8 for about 20 000km now and have had 2 oil changes. between those i have topped her of with a total of max 1 litre( half a litre pr 10000km)
Over to your problem, If it smokes on WOT i would assume its your piston rings or the dreaded alusil is worn out. It Could also be the valveseals but usually they will give you a puff of smoke when you go back on the throtle after "engine braking" from higher revs on a gear in manual mode.
