I'm using an old(er) Yamaha receiver that doesn't even have HDMI. It was part of a $300-$700 home theater in a box solution. It is delivering maybe 80-100 watts to every channel, plenty for a PC. A lot of the older receivers had analog home theater inputs, lately it's harder to find on all but the top-end absurdly priced units. So although it might be a crap shoot I'd check out Craigslist in your area for people looking to get rid of receivers with a decent wattage rating and analog 5.1 inputs. Unless you NEED to have this receiver do everything for you.
The receiver in my computer room has 2 PCs connected to it, of course only one can be connected to the analog 5.1 inputs, but such is life. After having three different sets of PC speakers essentially blow their amps or become otherwise nonfunctional I went the home theater route and couldn't be happier.
Other than that there was a product built by Creative to overcome this very problem you and I have noticed named the Home Theater Connect DTS-610
... although I'm not sure if this is sold any longer, but I have one, and it still works. Some have not had such great experiences with it, but that seems to be the case with most Creative Labs products in the last 3 years.