I would highly recommend a Grace Design m902 headphone amp and a pair of Grado RS-1 headphones. that will bring you in somewhere between $2000 - $2500.
just for reference:
http://www.gracedesign.com/
http://www.gradolabs.com/
just for reference:
http://www.gracedesign.com/
http://www.gradolabs.com/