Originally Posted by ntsnear
I'm running my S9 with Ultimate Ears Super fi. 5 Pro and that's just a joy to listen to the music with that combi. The S9 is good enough for your ATH-M50. I personally never use sound presets, always "normal".
So don't worry: You don't need anything else
You can't compare your ultra-efficient IEMs to a full sized phone like the M50. They have totally different specs regarding impedance and sensitivity. The OP was asking if he needs an amp to drive his phones, not how the S9 subjectively sounds with your phones.
Anyways, the S9 should have no issues driving the M50.