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To be honest, this should be self explanatory. If you're using the Windows Mixer, whatever the bit and sample rate you choose is what is fed to the DAC. If you're using Foobar2000 with WASAPI, then every PCM file you play are converted to the bit depth you selected and the sample rate is exactly the same as your sample file. If you're using DSD via DoP, then follow the wrapper format sample rate: for DSD64, I believe the PCM wrapper is set to 24/176 KHz and 24/768 KHz for DSD256 or Quad DSD. Or you can avoid DoP and just use Foobar2000's built-in filters to convert any DSD to 16 or 24 bits and your preferred sample rate selection.
As for USB modes, that's highly dependent on the module that the DAC uses. For XMOS, there's a very high chance that it's asynchronous mode. For Schiit Unison USB, I don't really know since there's no published data about it. For Chord DACs, their driver name already says Async so it will operate in Async mode and Chord provides Windows drivers to ensure that is the case
