<font color='#000000'>There are a number of ways to accomplish your goal.
Probably the easiest is to use a Soundblaster Extagy. This box connects to the PC via a USB cable, and provides inputs and outputs for both digital and analog signals. The unit also accepts commands from the inculded remote control, or your learning remote. You can set the box on top of your receiver, and use a long USB cable to connect to your PC, then use the remove to control the volume of the Extagy. It's not the same thing as controling the Sony volume directly, but it's easy to connect up, and will accomplish what you're trying to do.
Another option might be (I haven't tried this, so I'm unsure of compatability) the "Slink-e," which provides Sony compatable "s" control signals (in and out), as well as IR in and out for remote control of the audio gear from the PC, and vice versa. You can find a little more about the Slink-e at http://www.smarthome.com/1331.html.
Hope this helps,
Chuck</font>