Hi Zonk,
I'm glad to hear that rolling back to the old driver solved the issue, and allowed you to stream PCM @ 24bit*192kHz.
And I'm also glad to hear that, following a similar approach, you were able to solve the issue with the optical connection.
I was aware of your other thread ("NUC6CAYS high definition audio problem") and I actually had the feeling that you may have resorted to buying such a preamp to bypass the HDMI pass-through problem. That's the reason why I was so harsh in my rant against Intel above: they should have told you from the very beginning how you could achieve such bitrates via HDMI by rolling back the old driver (or using the generic MS equivalent). They could have warned you that such a workaround was not officially supported, or whatever else; yet they should have provided such a clue from the very beginning, and that's one month ago!
Instead they didn't provide any hint, and just told you that, whatever the original specs of such NUC promised, those specs had been repeatedly revised, and according to their latest revision it's absolutely normal and acceptable that in 2018 such a piece of equipment (with HDMI 2.0) is NOT even capable of supporting a PCM bitstream @ 24bit*96kHz. Isn't it ridiculous?
As for the USB/HD Audio issue, I'll leave it to Intel to provide whatever official feedback they have (if any) in the related thread, and I'll take advantage of this conversion here just to give you a few hints and ideas (I have a different NUC, and I don't have an external DAC/Preamplifier connected via USB: so I'm not sure that any of the following will actually help you).
First of all, my assumption (judging from the specs+photographs of the back panel) is that your DAC/Preamp has a very basic USB 2.0 input: as far as I'm aware of, all such equipment doesn't really need anything more than that to support HD audio bitstrams (24bit*192kHz stereo equates to a bitrate of just 9,216 kbps that is comfortably within the capabilities of USB 2.0).
On the other hand, if I'm correct, your NUC only expose USB 3.0 ports... but please note that, according to spec, it should also have a couple of internal headers for USB 2.0 directly on the board.
So, if this is actually the scenario you are dealing with, you currently have a normal USB2 cable connecting one of the USB3 ports on your NUC to the USB2 input on your DAC/Preamp. And of course your NUC USB3 ports are probably driven by an Intel specific driver...
Hence, one thing you may want to try is to select such driver in "Device Manager", choose "Update Driver", then "Browse my computer for driver software" and finally "Let me pick from a list of available drivers on my computer"...
If you happen to find any other suitable driver there (not from Intel) you may want to give it a try.
It's possible that if there's a generic MS/Windows driver this may easily solve the issue (it may not take advantage of the specific architecture, and thus put slightly more load on the CPU, but if it solves the problem, why not?).
The other thing you may want to try is to use the very basic USB2 connections available on the board and see if they'll do the job: you can locate such USB2 headers at pag.15 of the TPS.
Being older technology, hopefully Intel has stopped messing around with their drivers long time ago, well before they entered their current approach of cutting features (and specs) whenever something doesn't appear to work as expected... Plus, you will get a very basic, simple and consolidated USB2 to USB2 connection (so there's less chance the Intel driver is messed up to cope with backward compatibility issues, as their USB3 driver probably is, having to provide both USB3 capabilities and USB2+1 compability/support...).
Please note that according to the description at pag.22 regarding those USB2 headers "one port is reserved for an M.2 2230 Module"... whatever that means, and however it applies to your case, you should still have at least ONE USB2 header available.
So just get your hands on something like this for just a few bucks: at first glance, it seems to fit the USB2 header description provided at pag.42 of the Intel specs (please verify yourself).
Plug it in, connect a USB cable to your Preamp/DAC and see if a basic connection via good old USB2 solves the problem.
If it does, as I assume you don't want to drill or mess around your NUC case, you may want to check here: I didn't look carefully, but I assume they have a suitable "lid" for your NUC to expose the USB2 ports in an elegant way (and as they write at the top of the page, just contact those guy if you don't find - or you are unsure - of what you actually need).
Of course, if you think exposing such additional USB2 ports may be a "plus" anyway (even if it doesn't solve the problem), you can skip the preliminary test with a simple cable, and just purchase directly an appropriate USB2 "lid" that has surely been tested to be compliant with your NUC.
I really hope some of the above helps.
And of course, if it does, please let everybody know: I guess there may be people with other USB DACs having exactly the same kind of problems you reported...
