the m50 does not benefit greatly from an amplifier. sure, if your amplifier clips, distorts or has audio issues you will notice a difference if buying something higher quality but just adding more amplification power alone does not make them sound better like some other cans on the market. i own a pair.
i'm thinking this is your first pair of decent headphones and as such is the first you noticed such audio issues. this is generally two things: either A) poor quality recordings that you never noticed until now or B) poor quality dac/amp equipment.
clearing some misconceptions here:
- the m50 does not benefit greatly from a strong headphone amplifier over one just good enough to drive them. while quality is important excessive power is not as they do not respond greatly to such. some headphones do, these do not.
- most external dacs do NOT have an amplifier built in unless they say they have an amplifier built in (then they are called dac+amp, dac/amp, or similar). soundcards do have an amplifier built in to them (they are technically dac+amp+software type solutions if you want to think about it in simpler thoughts). some externals are separate dac and amp units while some are combined.
since buying an m50 for music at work i had to stop listening to any streaming below 128kbps as it was like listening to garbage since i could pick out the static and distortion. i never noticed on prior cheap headphones. i would try out some high quality audio files (highest quality ones you can find) and see if that fixes the issue before buying other equipment. it could very well be that you are just noticing poor quality files for the first time.
or, if that is not the case and if even high quality files have issues then its your dac/amp onboard soundcard components. onboard audio is at most equivalent to low end soundcards and while some is decent there are tons of boards with poor quality audio as well. either an external soundcard or dac+amp combination external would work and generally alleviate issues from onboard.
things like the creative omni, fiio e10k, audioengine d1 are all fine though not the only solutions.