You have 1 pair of stereo speaker, you then said you have a second pair. That's 4 speakers. WHERE is the .1? the subwoofer?
Modern PCs tend to have surround built-in, do u see center/sub jack(s) on the back? that's it. Otherwise you have to buy a sound card for the trick.
U don't need to have a subwoofer but 5.1 is that. Ur PC or new sound card should be able to play 4 speakers, won't be true surround but fake surrounds or stereo with back fill.