We gather that Windows Sound Properties in Control Panel only represents the capability of the Windows Direct Sound driver.
Most likely you don't want to use the Windows Direct Sound driver. It doesn't seem to permit the audio player application to change sample rates - it just uses asynchronous sample rate conversion and outputs the sample rate that is selected in the Sound Properties window.
To access the capability of a higher resolution device, it's necessary to use WASAPI or ASIO driver. An ASIO driver is included in the XMOS/Thesycon driver that you installed. WASAPI is incorporated in later versions of Windows. Operating with WASAPI or ASIO is not represented in the Sound Properties window. Note also that some standard sample rates may not represented in the Sound Properties window: 88.2kHz 24 bit and 176.4kHz 24 bit.
You can monitor the sample rate in the XMOS/Thesycon driver control panel:
Also, we've found that Windows Direct Sound driver will not send 32 bits PCM samples. If your audio player generates 32 bit samples then you must use ASIO or WASAPI in order to send full 32 bit samples.
You'll need an audio player that is capable of reading and playing high resolution files. Foobar2000 can be downloaded for free. We also test our products with JRiver Media Center.