It's highly likely that the 2.1 system, if it is priced the same as a 7.1 system, will be superior.
Simple logic decrees that if you produce five extra speakers in a setup without increasing the price then something has to give - most likely, in this case, to be the quality.
As the speakers are the final and decisive link in the sound chain, you need the best you can get and that also applies to the sound card etc.
There's an old hi-fi saying that applies equally here: Rubbish in, rubbish out.
You can always choose a 2.1 setup from the Windows audio properties setup.