I just bought a dt 990 premium 600 ohms and it runs at 85 windows 10 moderately loud for me, with no audible difference with an O2 amplifier it's just that it gets louder but way too loud, and sometimes cause static. Not sure if I just burned close to $180 canadian for an amp...
edit 100% my fault for not purchasing the headphones first then looking to see if I needed an amp.