The Windows / Control Panel / Sound / Driver / Configure / Test function does not really work if you select 5.1 output; from some channels you hear the test beep and for some not; I suppose it is something to do with latency..
Very short sounds don't always come through, or come through truncated; a better test is to play known 5.1 content and selectively mute channels in JRiver.
I tested this thoroughly with my setup, as below in my signature, and using the motherboard audio S/PDIF optical out, sending DD AC-3.
The speaker test function only works for the Left, Center, and Side Left when using 5.1 channels,
when I press the "test" button. Windows always delays the output in these tests, so it is necessary to run them at least twice to get sound output on all speakers, but running them multiple times still only plays those three speakers.
However, when I
click on the individual speaker images, test sounds are played from all speakers. The response is quite slow though, and if I click the speaker more than once, even with a reasonable gap between clicks, I only get one sound output. This is the Windows delay being introduced perhaps, or the receiver taking some time to respond. I can clearly see MC play each sound in the Action Window, and until that window clears, and for a little while after, a new click won't produce a sound. I observed that this sometimes meant I missed Windows Event sounds, if two or more events followed in quick succession.
This is true on my main PC/client system which only has stereo speakers as well. Only the Left speaker plays on clicking the "test" button, but both play on clicking the speaker images. I do get clipping or broken sound output for the test sounds on this PC as well, but not on the HTPC.
However 5.1 media plays normally on the HTPC system, and stereo plays normally on my main PC/client. While the "test button" feature does appear to be broken, this certainly isn't a critical issue.
One other feature doesn't quite match my system requirements. I have Bose satellites for my front Left and Right speakers, and Bose monitor speakers for my Side Left and Side Right. The satellite work best when they are not set as full range, or at least I think they do, and I'd like to try them that way. The Side monitor speaker are full range, so should be set that way. However I can't set them this way. If I select the fronts as full range, I can set the sides as full range. If I deselect the fronts as full range, the sides are automatically deselected and can't be manually selected as full range. Again, not a big issue, but a little strange. I can leave my fronts set at full range for now though.
Finally, on the HTPC I was able to reduce the Buffering setting to "Minimum Hardware Size", but I couldn't reduce the Live Playback Latency to anything less than the default "50 Milliseconds (recommended)" setting, or I would get clipping or similar effects.
Oh, also Windows also reported that the 20.0.25.0 driver was not digitally signed.
None of this outweighs the brilliance of having a WDM sound driver for any and all Windows applications to use on the HTPC.