yeahman68 and others wondering if the A900x need an amp,
After listening to M-50's for a couple of years with an Fiio E-11 amp, I began to really analyze the sound signature and started to turn down the volume and bass. I guess I am starting to become more an audiophile where I want to hear the music more how it was produced instead of how much it thumps. Thump is turning to be mud. So, I would really recommending NOT using an AMP with the A900x. Besides most players and computer have ways to adjust the sound signature "a little" instead of buying an amp. You will train your brain to listen more carefully... Amazing how the headaches went away and I haven't destroyed my hearing! Just my 2 cents.