Hi and welcome to the forum!
I've always liked Logitech for computer speakers. I have the
Z-2300 system, which is a 2.1 configuration and THX certified. On their website it says they retail for $179CDN or $169USD, but I paid less than $100CDN at TigerDirect. So for $300-$500 you can get an amazing 5.1 surround setup for your PC.
John