Well sadly the new 2016.11 WASAPI drivers don't work the nVidia audio devices
I decided to give it a shot since it would be neat to use my HDMI audio out (comes from an nVidia graphics card), which can use all 7.1 channels in my setup, instead of my S/PDIF out (comes from a Scarlette 6i6) which only uses 2. Sadly, no luck. In WASAPI shared mode it plays audio, but badly with lots of crackles, stutters and so on. The buffer isn't adjustable, it stays fixed at 10ms. In Exclusive mode it just doesn't work. It says that the hardware doesn't support the selected sample rate, even though I can verify it does (it is 44.1kHz, 16-bit) and says that on any rate you change it to, at any buffer length (it'll let you change the buffer to a wide variety of values). Same deal with WDM/KS. Works in MME mode of course but, well... :P
The card itself does know how to speak WASAPI. Using the WASAPI plugin for Foobar2000 works in both event and push modes and it is able to take exclusive control of the hardware and change both the sample rate and output configuration. By default in Windows I have it output 7.1 channels, 44.1kHz, 24-bit. If I load up a DVD-Audio file, it'll set the output to 5.1 channels, 96kHz and if I load an MP3, to 44.1kHz 2.0 channels (I can see data on the HDMI stream settings on the receiver). Seems to work with pretty low buffers, in event mod Foobar defaults to a 25ms hardware buffer, and I can set the software buffer (how much of the file it loads form disk in to memory) to 50ms with no issues.
I was hoping but alas, no luck. I guess the nVidia audio chipset is different enough from the Realtek one they were targeting as to not be compatible. Some day I'll find a good way to do surround output from a pro program but today isn't that day. Soundcards are such pests :P.