I’ll be in the same PC situation in a bit. I still need a new soundcard but just received my new receiver, the Onkyo 626 refurbished from Accessories4Less. The receiver is the key difference in SQ, but be forewarned, new receivers are a total pain in the rear to calibrate. I’m still fiddling with mine. And it just doesn’t seem to want to do old school ProLogic matrixing without massive channel bleeding.

Eventually better speakers would be a good upgrade; mine are much older but still killer for bookshelves. (Klipsch kg .5) My sub is pretty old so it can’t quite get as low as newer units but still packs a nice punch. From everything I’ve read, the goal would be to eventually have floorstanding full range speakers for the front mains.

I hope to soon get an HDMI capable soundcard so I can just run my PC into the receiver and playback mkvs etc. without having to reconvert for PS3. AFAIK this is the only way to achieve modern lossless codecs from PC to receiver.