Think that the root of the question is that there is resolution and frequency response that is coming through on the headphones and is lost on the speakers. This is entirely possible, and entirely something that could be corrected with a more resolving and/or fuller range speaker system. There are lots and lots of options for building a system that will provide all kinds of fidelity and resolution. That is, after all, the whole point.
Of course, it is also indisputably correct that speakers will never sound the same as cans. And if it's cans you like, trying to turn a speaker system into a replica of a headphone experience is likely to be a dissapointing trip. But it is certainly possible to squeeze a whole lot more resolution and fidelity out of any given speaker setup.
All that said in the abstract, without having any idea about what equipment we're talking about -- abstract is as close as anyone can get to an answer. High-end, resolving speakers with complimentary electronics can certainly produce as much resolution as headphones. You'll "loose" nothing. It will certainly be a different way of experiencing the music, but the same music is certainly achievable.
Finally, it's been said that there's a rough 10 to 1 price correspondence between comparable stereo v. headphone systems. It may well be complete nonsense, but there's at least a grain of truth in it. Which is to say, if you've got a $1k headphone setup that you think is just the cat's meow, it could run you north of $10k for electronics and speakers capable of achieving a roughly equal level of detail, fidelity, etc. So, all else being equal (not that it ever is), headphones are a much cheaper and more practical means of achieving high quality music reproduction. If you want to try to approach the same fidelity levels with a speaker system you certainly can, but it gets a whole lot more spendy pretty quick. They'll never be the same, but comparable is doable.
And finally, as mentioned above, if accurate reproduction is your goal, adding tone controls or equalizers or anything else into the circuit whose sole purpose is to CHANGE the original recording -- that is the exact opposite of accurate reproduction. It's not your answer.
