Picked up an older model Headroom Total Airhead on Audiogon for $50 to use w/ my iPod at work. Difference is amazing. I have a pair of Shure e2c that I'm using it with. Really opened up the high end of the Shures, and the bass is much punchier. I tested it with my Senn HD580s at home and it does an adequate (but not outstanding) job of pushing them....seems they are very inefficient. Definitely worth the cash if you can find a used one.
mitch