[wdmaudiodev] Single wave output miniport, multiple physical outputs

So this is kind of a weird one.
I'm working on a device that has a single wave output device; the playback data is simultaneously sent to an analog output and a digital output. The trick is that the analog output and digital output have separate volume controls.
Ideally, I'd like to be able to expose separate nodes and volume controls for the different outputs via the mixer API. Having a single volume control for the wave output is easy. What I can't figure out is how to set up my wave and topology miniports to display two separate volume controls.
I've tried creating multiple topology miniports as well as emebedding a second volume control within the wave miniport. I've also tried implementing a supermix node, without much success. 

I'm not even sure that this is possible.  Has anyone ever done this?

This is on Windows XP, with Vista support to follow.
I suppose one option would be to simply create a four channel volume control; that's less satisfactory, but would work. 

Matt

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