many who claim to eat 6000 cals a day simply don't, they may eat it for the odd day but to eat so much food depending on your size would simply overload your digestive system, you body can only process so much and the stomach needs to empty, if you keep trying to eat when you are full you will simply be sick.
Also the body can only assimilate so many nutrients, it also only manufactures new muscle tissue at a certain rate, everyone's different (genetics)
If you are not genetically predisposed to assimilating nutrients and creating new tissue, no amount of calories are going to help you
You need to work out a calorific intake that allows you to make gains but not get fat.