After talking with the Sennheiser support they have provided signed HDV 820 drivers; until they are posted on their website I have made them available here https://www.dropbox.com/s/44av42hgyvxsvi1/HDV820_USBAudioSoftwarePackage_3_32_7_87_WIN_SIGNED.exe?dl=0

The HDV 820 drivers for Windows available from https://en-us.sennheiser.com/digital-headphones-amplifier-hdv-820 are not digitally signed, therefore do not load in Windows 10 x64. Are there equivalent, signed drivers? As it stands today, I cannot use the HDV 820 in Windows.