The difference between a Musical Fidelity X-CANS, modified X-CANS and X-CANV8P is enough to justify a price range from £130 to £450. In the same way, if you are looking for improvements in sound quality a £130 amp will sound different from a £450 amp. The e-bay less than £100 headphone amps tend to be portable for use between ipod (or similar)and full sized headphone. I have not heard any but there are good reviews out there for the likes of the C-moy and Blue Jelly (second time today!). But what I am sure about, is that the more expensive amps will drive full sized headphones to their full potential. That is from connecting Grados and Sennheiser buds to a MF amp and an ipod. Horses for courses.