I can have my volume at the full 30 and they sound fine no distortion at all. I use stereo bluetooth headphones as in ear buds hurt my ears rather quickly, but I had no problems with the supplied earphones at max volume Lord Panos.
It seems to me that you've got the wrong headphones - perhaps some high-impedance and/or low-efficiency set. FYI, plugging in the 600-ohm impedance Beyerdynamic Tesla T1 into the Omnia 7, I definitely can't listen at louder than 27 and there's relatively little in the way of distortion.
Or, if you're misguided/dumb enough to be listening on full volume with a regular pair of head/earphones maybe you've blown the drivers.