Great amps which match well with HD600/cardas, in my experience:
The Maxed Out Home from headroom, preferably with reference module upgrades, and ideally a stepped attenuator.
The Corda Prehead.
Both amps are top audiophile and pair well with even the best of unbalanced (RCA) sources. The Maxed Out Home has a crossfeed which creates a more realistic soundstage and is a bit on the darker side, while the Prehead has a crossfeed which tends to create a more coherent sense of imaging and tracking but does not have as good of a soundstage. Both amps are built like tanks and get my recommendation.
You should use, ideally, a pair of Dimarzio M-Path interconnects if possible, unless you have something even better.
With one of these amps, and say a $2000-4000 source your full potential will be realized. I have one of the above amps and drive them through a $200 CDP because I ran out of money, but the performance gain from using a good amp is still there.
Cheers,
Geek