[ProtegeManiac]

So you're saying headphones don't sound that much different from earphones?

 
Not enough to worry about. Response being comparably neutral, and assuming the headphone chassis doesn't put the driver smack over the ear canals, generally the IEM would have a smaller soundstage although the imaging would be precise. The headphone would be slightly larger, many of the instruments would be slightly if not well outside the head. Unless you really care about imaging, it's not really a problem.