Don't let Airman mislead you. A HDMI out isn't a magical conduit that makes pure sound leave your computer. We went over this in the Titanium HD thread. Muxing takes place and adjustments your sound card may do to the stream unless the sound card has passthrough capabilities. A easy test for this is to see whether or not you can adjust the volume. If you can adjust the volume it's not a pure passthrough to begin with.
I'm not misleading- you're still confused. It's not a 'magical conduit', it's an audio path, and I'm really not understanding why that's hard to grasp. Sound is played through the OS audio stack and then sent to an output device- if it's HDMI, it's then forwarded to the receiver, where it's converted to analog using the receiver's DACs. The receiver may do some processing on the signal, which should be user adjustable.
What isn't used are the DACs and any sort of analog components on the sound card. Sound cards aren't just DACs though.
Actually, they are. There is no more 'hardware' sound, outside of the corner case of OpenAL- all 'mixing' is done in software. The sound card really is just a DAC (and ADC for mic and line-in). Everything else on sound cards is either unused (Creative's XRAM, for example) or is part of the analog path- which is everything on a non-Creative card like a Xonar aside from the DAC/ADC.
I'm not trying to offend you, but you are wrong here; there is literally no use for a 'sound card' when you're only using HDMI. Hell, even if you used that Auzentech card with HDMI pass-through, the only thing you're gaining is the ability to use Creative's software! That's it!