You didn't. There's a reason it has been one of the most popular HiFi headphones for over 20 years, mine was made in the late 90s and still works very well. Despite having more expensive and technically superior headphones the HD 600 is my daily driver. It's ergonomic and very well tuned, I run it with only a +3dB low-shelf.
That I was. The HD 600 works fine with the european Apple dongle (500mV output), normal listening level with that is at 45% volume setting in Windows (well, normal for me, YMMV). Any source able to provide at least 500mV will be ok, 1V would be plenty.
By easy to drive I also meant that the high impedance means that the HD 600 draws little current and high output impedances don't cost too much effective power (voltage divider).