generally the m50s dont hae an issue being powered by most devices (including my smartphone, ipod classic or laptop) but in some cases a device might not output enough juice to make full use of them. this appears to be the case here.
you have a few possible fixes:
-buy a soundcard with a decent amped heaphone jack
-buy an external dac+amp (highest cost but highest sound quality solution)
-buy just a headphone amp and use your onboard audio for the dac (not as good as the prior)
i've had my m50s for years and for the price its hard to beat them.
i7Baby :
Newer mobos have better sound.
not necessarily. some boards ship with fairly decent onboard (like the asus maximus series) while others ship with fairly mediocre realtek sets (most low or mid tier boards). actual performance can vary quite a bit across the board between models. as far as comparing new motherboards to old motherboards i doubt a low end mobo will beat my $350 rampage iii for onboard sound. even an old higher end onboard soundcard is going to trump a low end solution thrown on a budget board. quality is important too not just how new something is.