What is the max number of volume "blocks" I should have so that I don't cause hearing damage? Does each block roughly correspond to 10dB of sound? Would using a higher resistance headphone make a difference(like a pair of 64ohms HD 280 pros) in the actual dB of sound. I cuurently listen at a max of 4 or 5 clicks of the volume rocker( or 5 "blocks"). Is this safe?