Feilong4
Headphoneus Supremus
It's DAC not a amp.
Welp, that shows you how much I know about Amps and DACs.
Take a look at these. In your price range and pair great with HD600 and just about anything else.
http://schiit.com/products/magni-2
http://schiit.com/products/modi-2
Do you know if the previous versions are good as well? I don't how how the newer versions are different from the previous ones.