If you have a pair of these (not 2 pair) then each speaker is connected to its own channel (left or right) and not in parallel. Assuming that your budget is low I would suggest that the best option would be a good used intergrated amplifier or stereo receiver. You can try Best Buy for a cheap new stereo receiver.
If you had the budget a new integrated amp like the Cambridge Audio Azur 351a, which has a USB input for your PC, would bypass your audio board and give you a big improvement in sound quality as well as being an great entry level unit to high end audio.
So what kind of wattage and resistance should the amp or receiver I get have?