To reduce bass performance, you should move the speakers further away from any walls.
The mid-range and treble are quite difficult for the speakers to reproduce, and I've found that vocals on speakers I've used, be it in music or movies, can sound muffled. The better the speaker, and most of the time, the more expensive the speaker, the better the mid-range/treble will be. You should also know that damping your room acoustically with a carpet, rugs, bookshelves, etc. can help to improve sound quality.
The treble controls can do more harm than good, because lower quality ones (ie. most of them) will affect frequencies other than the ones you're interested in. I'd leave them alone unless your listening at low volumes and need a bass boost.