Thanks a lot, you're my saviour. I lost half a day trying to use this as a DAC. Then I stumbled upon your solution. So I registered right away just to give my feedback.
Like you I'm using Windows 8.1 Pro 64bit and just like you I had the same problem. The driver installation went fine after disabling the Driver Signature Verification but no sound.
Now I got it working thanks to your detailed post.
So it's a common issue I suppose.