Many are aware of, or using the FiiO E3 headphone amp. The new bigger brother, the E5 is now finally available to pre-order.
Check out the description and links in the Accessory board.
(Disclaimer: This is not spamming. There has been a great deal of interest in this product on various boards. I am only sharing knowledge of it and providing links to another post on this forum. I have no financial interest in it or DealExtreme.)