This is my personal opinion.
If the speakers remain same. Changing the DAC/Soundcard wont dramatically improve sound. Its difficult even for a trained sound engineer with a blind test.
Sound cards are not like graphics cars which can show quantifiable improvement (unless you use a audio analyzer).
I prefer to use balanced audio cables as its less prone to interference. I buy interface/sound card based on requirements. Better mic preamps, SPDIF digital outs, mixer options, DSP effects..
If all you do is listen to youtube audio, buying a sound card to improve audio quality is useless. Now if you talk about lossless audio like flac or really crazy DSD files where one song can be 400mb and have ears which can recognize pitch then yeah a good sound card would be good upgrade.