Aren't the mdr 1a phones 48 ohm? If so then 50 ohm would be no problem. 250ohm dt990s however are too quiet. EDIT: MDR 1As are 24 ohm. So I don't know. EDIT 2: just tried with my 62 ohm K702s and at full volume (30) it was 'loud enough' but you'd probably want some more headroom, especially in a loud environment like a plane. BTW I have the Australian version so I don't know if it's volume limited or not.
2/18/16 at 3:24am