Newbie question regarding stereo headphones...PC

That sounds like an analogue connection.  Dolby headphones usually utilize one optical cord which carries the 5.1 sound in digital, and passes it through a decoder, which then carries that processed 5.1 sound through the single 3.5 cord that your headphones use.  If it's coming from the computer soundcard, then you're just outputting the dolby headphones signal from there to your headphones via the 3.5 cable.  In that sense, it's not true surround sound in that there's no dedicated channels, but it's a virtual surround sound that takes an actual surround sound feed and processes it for stereo headphones.