The A340-600 has four engines, not six. But the point is still true with, say, a Boeing 787. Here are the figures for the 787-9: maximum takeoff weight: 560,000 lb; maximum landing weight: 425,000 lb [1]. In case of an emergency the pilot has to get rid of fuel before landing if the airliner is above maximum landing weight.

[1] Figures given in pounds on wikipedia, the kg version looks like a "dumb" conversion: https://en.wikipedia.org/wiki/Boeing_787_Dreamliner#Specific...