If the speakers are more than a foot or so form your ears, you have to expect a different sound. The soundwaves are traveling through the room and bouncing into everything there - the headphones are a direct link to your ear drum, and therefore - you get a "sterile", unrealistic sound. It's very spoiling to use cans, but it's NOT the real world - so my advise is to move the speakers closer to your ears - put them on good solid studio stands to isolate the vibrations from the floor and tweak the mix till you get the tone you KNOW you want. You should only have to adjust the master EQ one - then everything should be relative.

Remember:
Success is relative....... the more success, the more relatives !