Sound Card vs Sound Card (headphones)

[Soulwrite]

I have a Asus XONAR DG8786 and a pair of Sennheiser PC323D Headphones. The Soundcard is connected to front and rear Mic & Audio ports, however the Sennkheiser comes with a 'USB soundcard" which it can connect to however this bypasses the pre-existing soundcard.
Which is better & what would be best to use? Advantages/disadvantages?

 

[justcallmetom13]

NEVER BUY A SOUNDCARD THAT GOES INTO YOUR COMPUTER.

Buy a DAC or an AMP, quality headphones, a quality mic for the best listening/recording experience.

The Sennheiser, while not better than any external DAC and AMP combo, would still be 10 times better than a soundcard that goes into your computer.