Which generation Zune do you have? The Zune 1G uses the Wolfson WM8758, the same as in the iPod video. Thusly, you'd theoretically just do the diyMod/iMod trick to the WM8350 and you've got pretty much what you need. I believe the chip is on the other side of the board. The Zune 2G uses the Wolfson WM8350, a much more complicated chip than the WM8758. The datasheet for the WM8350 isn't anywhere I've looked, so you may have to email the nice buggers at Wolfson. Maybe if you opened up your Zune and gave us some sweet pictures, we could get a bit further than hypothetical predictions.
Scratch the WM8758 and replace it with WM8978 (see Zune vs iPod vs ZVM Comparison Chart). At any rate, I can't see the Wolfson anywhere in the photos. Doing a bit more research, I've concluded that the WM chip must be at the top centre left a bit.
It's really hard to see, but checking the WM8978 datasheet, the outputs are OUT3 and OUT4. I'll be off to update the diyMod thread now.