No audio option, not that I know off. And I checked the manual that specifically says that a fibre optic or SPDIF cable must connect the decoder to the TV or AV to enable 5.1 surround sound. The HD PVR does not have any options to set a HDMI connection. Only 2 settings for surround sound: AUTO or FIXED. The other option is LANGUAGE option that allows you to set the "second language" or "surround sound".
Way in the beginning, when the HD PVR was first released, it didn't support audio over HDMI but that was corrected by an update soon afterwards, they just took a long time to correct the manual. It definitely does DD over HDMI. Go into Advanced Options and then select DSD Upgrade to get the latest update.
EDIT: Oh, sorry gbyleveldt, didn't see your reply.