FYI, I have the Sennheiser HD570s. I really, really like them. I borrowed Adam's old headphone amp for far too long, and couldn't really tell a sonic difference between the amp and the straight connection to an ancient discman. HOWEVER, there was a lot more headroom (by this I mean available volume). I'm seriously thinking about getting a headphone amp for my computer/iPod listening...
When I listened to a very nice looking Creek amp in an audio store run by jerks vs a less nice looking, cheaper Creek amp, the first seemed to have less hiss on the volume pot.
