the ath-m50 does NOT require an amp and does NOT sound better with an amp.
is there a difference? yes, but it is very slight and not worth forking out money for an amp.
will it benefit from a better soundcard than motherboard onboard sound? yes, it likely would since onboard normally isnt great but its not going to be a huge leap. going with something like the dx would give you virtual surround though.
source: i own a pair of m50s.
now... there ARE headphones (dt770pro-80, hd598, etc) which do sound better on amps even though they might not need one
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the reason i suggested a modmic is that it literally has a sticky pad you adhere to your headphones (it is removeable if you wanted) and then the actual boom mic mounts to that pad with a magnet. its totally removeable for when you want headphones and not a headset which makes it incredible convenient.
if you click on the headphones guide in my signature and scroll down i have an article on how to use ANY boom mic and mount it to a pair of headphones although its not the prettiest solution which is also why i suggested the modmic.
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ALL headphones require amps however the amp is built into the soundcard. in the case of normal headphones the amp is at the source (pc soundcard or external amp) and with usb headsets it is integrated into the internal soundcard on the headphones themselves. quite frankly i think you can get better sound out of a pc soundcard than a headset internal soundcard
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now i have a question... if you can ignore amps and microphones for just a minute....
do you require surround sound in your headphones or is stereo sound fine?
if you do want surround, is virtual surround okay or do you need multiple driver headphones?
on this page
http
/www.head-fi.org/t/534479/mad-lust-envys-headphone-gaming-guide-update-7-9-2014-ultrasone-hfi-15g-added i do believe there are a few linked videos which allow you to hear what virtual would sound like. the page does take forever to load even on highspeed though (lots of content)
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as far as signatures go... all you need to do is have code like this..
Code:
[img]www.host.com/image.jpg[/img]
to include a signature photo. it should be on a fairly fast host (i suggest postimg but tinypic or other hosts work too)
if you want, i can create a signature for you if you let me know what anime you want. i did the same for RazerZ before. they are rather simple but this is what i made for him http

/postimg.org/gallery/2t0dzes56/ from scenes cut from anime i own.