I have the gigaworks s750, 700 watt system, sounds bloody brilliant. Sadly nobody is making 7.1 PC systems anymore. Your best bet is go HDMI or optical to a good quality receiver. Denon, Harmon Kardon, etc.
Beauty about the gigaworks system is it's basically an amp and sub, with a center and 3 pairs of satelites. They use normal speaker wire, so if I blow any of these or if I just want to upgrade I can later buy different speakers like bose etc and just connect them up. If I blow the sub, the box is huge so I have plenty of options for replacement, I imagine I could even use automotive brands like Rockford or JL. Also the gigaworks has a remote so I can adjust the volume sitting far away as I sometimes do when watching movies.
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