Aha...I think...I'm starting to get it. Assisted by this diagram from Subaru:
http://img241.imageshack.us/img241/2...diagramiv7.jpg
As well as Harvey's illustration, I think that's right... the planetary gears have the ratio for the front and rear. Connected through to the front sun gear is the clutch, which essentially "overrides" the planetary gear ratio by introducing a load onto the rear output shaft. That load from the rear output shaft is fed through to the front transfer gear, where it is added to the torque already gained from the front via the planetary gears.
It all makes sense if the front transfer gear (front, in yellow) is connected to the input shaft (in green). This way, when the clutch (rear, in yellow) disconnects from the rear shaft (in red), torque is still fed to the front via the transfer gear (front, in yellow), but more is fed to the rear through the planetary gears' (blue) ratio.
Sorry if that sounds overly complicated, but if I don't get really deep down into specifics, I won't be able to wrap my head around it. I'm trying to hold a 3D model of the mechanism in my head, and then move the gears and clutch... so yeah...