Hi,
Not easy and not guaranteed,
- check if the integrated sound card of the motherboard is disable and the drivers completely uninstalled, (if uninstall => reboot after)
- check that the new sound card is the default in the 'Sound' control panel of Windows 10
- check that the ASIO is not activated (if it is? I do not know this card)
- uninstall drivers then reboot PC
- install the latest drivers
- check for Resolution and sampling rate: 48Khz / 24 bits.
test Davinci resolve Preference to enable use system audio output. (required)
And if it really does not work, try the drivers of this page
http://maxedtech.com/asus-xonar-unified-drivers/(Asus drivers for W10 are from 2015/10/23)