Actually you might not need to use your sound card, especially since your receiver accepts audio from HDMI.
The question is what graphics card you have? HDMI accepts both video and audio in the same cord. It's actually better than using optical for audio due to the limited compatibility of optical. The only reason I would use a sound card for is with analog outputs, and even then, many motherboards have more than sufficient audio output. Unless if your HDMI port on your card doesn't accept audio, it be better to use HDMI for this purpose.