those are 8ohm and 100w rated speakers which means that you will need an amplifier capable of that rating or perhaps just a tad more.
this could be either just an amplifier or a dac+amp. the first would use your soundcard and an analog (3.5mm) connection while the second would likely use either usb or optical spdif and will pretty much bypass your soundcard.
normal amplifiers are available in many quality grades from very cheap (about $10) to models which are very expensive (over $500). it would be best to match the quality of the amp to the quality of the speakers. if you wanted to go with an external dac (digital analog converter... basically what is inside a soundcard) and amp (also in a soundcard) combination then you have three...