I'm using a Musical Fidelity X-Cans II on mine and it sounds great, just make sure that you upgrade the tubes.I used to only used them on my SF Line 2SE but a seperate amp really does make a difference.
But if you really want a great headphone amp check out the top of the line from Headroom.
But if you really want a great headphone amp check out the top of the line from Headroom.