Easy to drive does NOT mean any amplifier with enough power can drive it WELL.
From my experience, the low impedance high sensitivity phones are the hardest to find a matched amp since it needs a lot of CURRENT. (P = I^2*R, so to output the same power, low impedance hp needs more current. I know it's too simplify but that's an easy way to look at it. I don't see why the output power matters that much to some people)
For high impedance phones, it may need high output power to have sound but generally they are really easy to drive(despite the picky HD800), but for a long time, I have had a hard time finding a good amp for planners.
As far as I know Dr. Bian Fang is one of those who will laugh at people driving headphones using their computer sound cards, ( yes, I go to Chinese hp forums a lot) and from how much money he spent on the EF1000 you can tell what's his attitude towards driving his headphone. I am not saying that some budget amps are bad or something, and I believe there are many overprice amps in the market so price doesn't mean anything. But really, driving a flagship planner like this using a $100 dollar amp? Sounds to me driving a Ferrari but get the regular gas and a set of $400 all season tires.