|How does it sound with other sources? You should be getting perfect audio, since HDMI is a purely digital connection. If you haven't already done so, run the receiver's audio calibration program. Speaker calibration can make a huge difference, especially in acoustically challenged rooms.|
I don't know what you're using to decode audio on your PC, but foobar2000 is easily the best music player, and LAV Filters + MPC-HC does a great job with surround formats. If you have MKV files with TrueHD or DTS-HD Master audio, LAV will even let you bit-stream the raw data directly to your receiver, bypassing any software decoders.
Also, if it's an older receiver, you may want to try running an optical cable to it. Some older receivers (like the Onkyo I once had) sound slightly better playing S/PDIF sources. I recently switched to a Pioneer receiver, which does a (much) better job with HDMI audio than my old Onkyo.
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