I think that what you want it's possible with motherboard that supports 5+1 channel mode.
in this case you can control the volume of rear, front and central/sub.
I've recently found this software for via-epia motherboard.
look my last post
I don't think it's possible set up predefined configurations (for example single guider, guider with passenger...) to do this, probably it is needed some development on the front ends... but I don't konw if it's possible...