You might find this useful: http://www.head-fi.org/t/668238/headphones-sensitivity-impedance-required-v-i-p-amplifier-gain
Not a direct answer regarding your headphone, but it should give you some idea on what kind of parameters you should be looking for.
Don't really think the heat/current issue is correct with headphone. The power requirement on headphone is usually so small that the heat generated is negligible. With a 600ohm headphone, the current needed is also less demanding than, say, a 12ohm headphone. It is not the same compared to speaker.