I use a pair of Alesis M1 Active MK2 studio monitors for my PC and if I want surround sound I'll use my HTPC with the Pioneer/JBL/Polk 5.1 setup.
The Alesis have very good imaging and I do most of my gaming, movie, and tv watching with them. they also play loud and clear at levels that hurt your ears.
Do you actually have your 5.1 setup you use now with the speakers in the proper place? I see a lot of people have all 5 speakers sitting on the desk facing the user which defeats the purpose of surround sound.