I have ROG Xonar Phoebus Solo along with HyperX Cloud Revolver. Now this headphone's rated impedance is 30 ohms and naturally in headphones setting I selected Normal Gain (0dB for <64 ohms) since it falls into that category.

My question can I use High gain (6dB for 64 to 150 ohms) without damaging my headphones, does it damages anyway, in short duration or in the long run? Can I go even higher if needed (just curiosity as 6dB is enough imo)

Edit:
Also in the spec sheet found @ http://www.hyperxgaming.com/datasheets/HX-HSCR_us.pdf there is this bit of info:
Input power Rated 30mW, Maximum 500mW
so in a sense it may be possible that it can handle more voltage sent by the sound card and driven at a louder gain no? I just do not know what 6dB more gain equates to in terms of mW. I do not want or need to reach max mW too since it would be too loud anyway and certain to have more harmonic distortion.