Thanks all. Some good tips there, I'll def consider an amp.     I've heard that when some people buy headphones they leave them overnight with white noise playing at a high volume. Is this something that has a bit of science behind it or is it just voodoo?

Just bought some brown Momentum Over-Ears and I am not very impressed. When I turn the volume up full (or nearly full) then the treble starts to get hissy + clipped. Also I've found the vocals can be get quite muddy and lack the definition and clarity that I have experienced with other...