K712 is not difficult to drive but high quality DAC is a must to get best of it.
I recently auditioned the Airist Audio Heron 5 headphone amp, for 10 days, that puts out 5 watts into 32 ohms. So suffice to say it has gobs of power. I found there to be a significant difference in speed, weight, and attack of the music compared to a portable audio source. I unequivocally agree that a quality DAC is really important too though as the K712 are quite revealing.