...1) can u mix on headphones and expect the mix to sound good on speakers...
The debate about using headphones for mixing will probably go on forever. I feel that the answer to that will always be subjective based on content, skill level, and expected results. Many headphones do tend to give us a false sense of separation, depth, level of effects, and sometimes even volume. Our perception of physical positioning is reduced significantly due to the headphone's lack of movement in relation to our ears. The space between the drivers and our ears (the room) cannot very well be treated for acoustic anomalies or inconsistencies in driver response. (...and too many headphones do have horrible driver response.)
Content:
It may be quite easy to get a decent mix using headphones if the number of tracks is small and they are good quality tracks to begin with. Some raw tracks tend to "mix themselves" with little effort compared to others. Many people have gotten good mixes using headphones, but we don't know if it was by chance or not.
Skill Level:
Can a total newbie figure out how to at least set two instruments at similar volumes using phones? Of course! Can a total newbie figure out how to mix an entire band? Well, yes but, it probably won't sound any better than if he had used proper monitors. His lack of skill may be more of a problem than the fact that he is using phones. EQing doesn't become any easier using headphones either. You've still got to develop good skills and technique no matter what you mix on.
Expected Results:
Just as with monitors, experts expect better results than rookies. If you don't know what to listen for in a mix, you may be satisfied with anything. If your goals are to simply set levels in the mix and call it done, then the cans may not be a problem. If you only want to tweak the "esses" in common speech, they may be a good tool to use. If your goals, however, are to make a world-class platinum-selling album of Nobuyuki Tsujii playing with an orchestra in Carnegie Hall, you may want to rely on more than just phones alone.
Again, results can be as subjective and circumstantial as are our personal tastes in visual art and cooking. There is little way to measure and compare the level of success that one might have using headphones. As a general rule, we warn against it mainly for the reasons that I've mentioned in my first paragraph. Also, the sound quality of headphones varies as much as it does with speakers. If you decide to use them, read reviews, listen before you buy, and choose carefully.
