paulruk> earphones sounding flat (=linear) does not mean they are bad at all. All monitoring speakers and stage earphones have flat output. Use a software DSP before the output (for instance DSPManager) if you want louder low's and high's. Flat output is usually best when you want to get all the mediums in classical music.
I've got westone UM2, linear output, DSP Manager does wonders on house / rock music.