Volume control issues

[Grasshopper]

I'm a longtime user of Sage and am just getting round to attempting to resolve some minor niggling issues. At present, my quest is to simplify my audio volume control.

I output audio via spdif to a Dolby Digital receiver, which powers my 5.1 speakers. I'm using nVidia Soundstorm on my motherboard. What this means, I think, is that normal TV watching is upmixed to faux 5.1, but volume is controlled within the PC. However, DVD audio playback is passed through straight to the spdif, and it's not possible to control volume from the PC -- that has to be done at the receiver. Currently, this requires a separate remote -- and that's what I'd like to fix.

So, my first question: Is it possible to have the PC process the DVD audio stream so that volume is controllable from the PC? Will I experience a loss in audio quality? Will the audio stream remain 5.1, or will it revert to stereo and then be upmixed to faux 5.1?

Now, assuming that the answers to my above questions lead me to conclude that I'm better off sticking with passthrough, I have a followup idea. Currently, I'm using a Snapstream Firefly and Girder to control my PC. I have a USB-UIRT that I'm not using and I'm pretty sure I can configure Girder and the USB-UIRT to control the receiver's volume via the Firefly. But, is it possible to do this and still retain the on-screen volume display within Sage (or within the PC at all)? In other words, I think I can completely offload all volume control from the PC, controlling it at the receiver instead. What would be ideal is if button presses on the Firefly showed up as volume level changes onscreen in Sage, but didn't change actual audio output volume. Currently, this is exactly what happens during DVD playback. Is it possible to get the same thing to happen when watching TV?