I own a Headsave PPA, and have nothing but good things to say about Norm at Headsave, the sound of his amp, and his customer service. I own Grado SR225's, and I asked Norm to recommend me a home amp. He firmly told me that if I could swing the PPA, that I would hear the quality and not regret it, and he was absolutely right. If the PPA is too much at 400-ish, then there is the Elite SL, a pimeta home amp in the 200-ish region. If you are dead set on a MINT amp, then stretch a little and go for the Headsave MiniMe, which is a MINT built to be a stationary amp run from wall power, so it has all of the possible MINT sound improvements enabled (which use too much power for an amp run from a 9v battery). The MiniMe (maxed-out MINT) is just above 100. Fewtch, one of the Headphoneus Supremii, has given it the description of providing a warm, sweet, clear and liquid sound - very pleasant.
Back to the PPA: I recently auditioned the HD600's on my PPA, and I would call the combo exquisite. The PPA brought out the expressiveness (I would say liveliness) of the 600's, and their lovely smoothness and detail. I've got a pair of the HD600's in my future sometime over the next year. I'm saving my shekels now.
Norm at Headsave has also given me free advice about my home sound system, and he is just a knowledgable and helpful audio professional. He and his amps have got a very good reputation at Head-Fi.
To recap the answer to your question:
What's really going to be enough amp for your HD600's is the PPA. The Elite SL (Pimeta) and MINT amps are old enough to have threads on them with comments on how they drive the HD600's. The Headsave amps will be good representatives of these species of DIY amps. Do a few searches on titles for the terms pimeta and mint and check out those threads.
