Is there a difference between DAC only and preamp? I've tried configuring by connecting power while keeping volume know pressed, thus entering settings menu but I don't see any difference. Volume is still controlled through the volume knob in DAC mode. And I also don't see sample rate if not when changing it. Volume is what remains visible for both settings of "d", 1 and 0.
Windows 10 here. Do I have to install the specific drivers for it? I had a Topping D10 before and when I disconnected that and connected the DX3 Pro (v2) it recognized it just fine and Topping control panel sees it with no problems...
I connect it to iLoud Micro speakers who are powered speakers, if that makes a difference somehow (don't think so).
Running in DAC mode only bypasses the pre amp circuits, since it is not a dedicated well built pre amp, maybe the circuit is not that great? I may be wrong, but it is known from the Topping D90, DAC mode definitely have better quality than running in the pre amp mode due to the same reason mentioned above.
And for windows 10.. It is best if you download and install the latest XMOS USB driver from Topping Website for your DX3 pro. Those driver will also significantly improve your sound quality due to not using Window's driver which is not dedicated written for the DX3 Pro and may not unlock it's full potential. Also, depending what music player you're using it with, try to use ASIO instead of WASAPI or windows driver
As for the D-0 and D-1,
From my experience. After you change the settings to D-1, press and hold the volume knob until you see "8-8" to save the settings, then turn on the DX3 Pro and take your Topping remote, press the headphone button, and then press the line out button again. Then I see sample rate only and volume control is disabled. Try it for yourself. I hope it works for you