On their website:
“Windows 10 and Apple OSX version 10.6.4 and above natively supports USB Audio Class 2.0 – no driver install is required.”
I have windows 10, so I think I don’t need to install the driver
If you don’t install the driver you only get the 32 bit depth modes, and those can cause issues in some windows apps.
what does this driver do?
A driver lets “communicate” the OS to access hardware connected to the PC.
Before new OS like windows 10, pc users have to use cd with the drivers for each hardware microphone, webcams, Graphic cards ( graphics card came with a cd with drivers).
Now, most modern OS automatically looks for drivers over the internet and update your peripherals to the latest driver.
Sometimes certain peripherals drivers used from Windows are not the latest ones or in some cases the wrong ones, which could affect the functionality of the devices. Like when you open Nvidia game ready that looks for the latest drivers for you and tells you to update.
What our friend @Deleeh is trying to tell you to look for the latest specific driver (xmos web site, for latest) for the sdac-b hardware. That way we could discard the possibility of driver malfunction.
We are trying to solve the trouble with your DAC. That is why we are suggesting things like changing cables, switch inputs, verify from the software end on your pc, and some other stuff. It has happened to me and some other users when a simple input switch or what happen to me when I bought an RCA cable from a reputable seller (inverted channel) mess my setup 
I see!
There are two available drivers for download on that website, which one should I download?
Edit: oh, probably the one that’s free 
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This free version has a “Beep tone every 5 minutes after 60 minutes”
Anyone know about this? This would be very annoying
I have no idea. Better stick with the windows one lol. How does your audio chain sounds? Any better or different after a day
Actually, I fiddled with Oratory’s EQ presets to my liking and I am enjoying music again 
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BeBe -
I’m running essentially the same setup - Grace Balanced SDAC into a Loxjiie P20 driving a pair of HiFiMan Devas setup for balanced operation via the front 4-pin XLR connector.
You’re right, USB ‘2’ does sound the better of the two USB options. When I took a look inside of a P20, it appeared that they had prioritized the XLR signal chain over both the single-ended and balanced headphone jack outputs - so I built a pair of 3-wire XLR jumpers using $8 worth of connectors from Amazon and some wire I had in my junk box.
This setup works well & sounds so decent, that I’m planning to upgrade the P20 with new 5670 tubes and an op-amp swap. This little amp’s basic circuit topology, layout, and parts quality is far, far better than it’s price would suggest - it’s like the audio folks designed it & then the marketing weasels brought it in at a price point by using the cheapest tubes and op-amps they could source.
All the more modding fun for us …
Cheers
Jim - KJ7QT