I'v been using headphones since the early eighties and have always settled for a maximum budget of around £100 and thus far have enjoyed myself enormously. Whilst checking out an headphone forum, I came across a section dealing with headphone amplifiers and was amazed at the variety (& price!) of some of these units - does the use of such a unit offer significant improvement over conventional means of using headphones? Can a decent one be bought for around £100-£150? would I have to buy a more discriminating pair of headphones to make the most of these?