"Built in headphone & microphone jack pass-through"
Pass through means you plug a cheap low quality cable into the cheap low quality socket on the back of the pc, plug the other end of the cheap low quality cable into a medium quality socket input on the keyboard and then plug your microphone or headset into the medium quality output socket on the keyboard. Congrats you have paid $100 for two extension cables.
I would expect initially when all the connections are new and clean to hear no difference, and over time for the connections to corrode, get dirty, loosen up and the sound to degrade if not disappear from time to time.