Random question, but is audio quality better on PC if you plug headphones into the speakers or into the tower directly? Or does it matter?
Quality of sound for headphones (assuming a good set of headphones and not some $20 junk) will come down to DSP (especially for virtual surround), an AMP and the DAC.
If you are grabbing the output form your speakers, you're probably getting an amp boost thanks to powered speakers. Who knows if it adds noise or distortion though. You probably won't be getting virtual surround via that output though unless your DSP solution allows it. The best solution is a good quality DAC with a low signal to noise ratio that is isolated from other components in your PC as much as possible, a good amp that can power your headphones well, and a versatile DSP to get the source to what you want.
It's why (well some of the reasons why) sound cards use dot be relaly popular back in the hey day of PC gaming audio. Now a days, since hardware accelerated audio appears to be a thing of the past (although it may be making a comeback thanks to things like Steam Audio) and VR, an external DAC and amp are all the rage. I swear by my Soundblaster x G5, for example. But I did also loved my Soundblaster Z and before that my Asus sound card.
A good pair of Sennheiser (or similar tier headphones) with an open back design (for better sound stage, highs and mids), plus a good sound card or external amp + DAC = sound heaven. Add a game that does a full 3D soundstage + physics based sound effectst like occlusion, materials interaction, and propagation and you sir, are in the future. I don't think many games do this, or do it well. The only game off the top of my head is Overwatch it it's ATMOS solution.