Do you what to have the surround sound speaker asswell? or just the front and subwoofer? If you just what to use the two front speaker this will work: http/www.ebay.com.au/itm/180W-180W-2CH-12V-Small-Stereo-High-Power-Amplifier-for-CD-MP3-Car-Audio-Home-/400586923881?pt=LH_DefaultDomain_15&hash=item5d44d75f69.
Note: each channle is about 7 watts each and your speakers are 40w each so they wont go to max volume but for a pc they will be good.
If you what to use all 6 speakers you will have to make sure your motherboard has the right out puts for 5.1 sound and if it doesnt you will then need to get a sound card. you will also need an ampliefer wich are quite expensive.
so like americanaudiophile said it would be cheaper and easier to just get a logitech pc speaker system if you whated to use all 6 speaker and if you just what to use 2 you will be good to go with that ampliefer that a linked, i have that one hooked up to my 2 front speakers and it works good with my pc.