It means that if your 2.1 system has a single stereo input you set the pc to 2.0. You would connect this with a single stereo cable.
If your 2.1 system has separate left/right/sub inputs you set the pc to 2.1 and connect with the above and a 2nd connection to the sub out of the sound card.
2.1 is NOT stereo. It is 4.1 with an electronically simulated set of rear speakers. Using a stereo driver with a 2.1 sound system flattens the sound, and NO, the woofer never gets involved at all. I had mine working after I updated to WIndows 10, but it took a long time to find the driver, but Windows 10 replaced it two months later, after I had forgotten how to fix it. In the past I have been able to use a 4.1 Dolby setting, and everything worked, but WIndows isn't being fooled by the emulation firmware, and won't play the rear channel unless it sees the speakers.