For 5.1 I get on fine with my Xonar DX/XD and Logitech X-540. The sound card certainly improved analogue out from my previous onboard P67 era realtec.
For higher quality 5.1 you will need digital out, probably real time DTS/Dolby Digital Live, and a decent amp and speaker set (with a sub). It's a lot of outlay but the benefits are large. My sub should be coming tomorrow to complete my setup (XLS200-DF).