The video below will instruct you on how to update the firmware in your AT-D878UV and AT-D878UV PLUS. The software and firmware download can be found below in the "Latest CPS Version Download" section above the video. If you don't want to update to the newest firmware, previous CPS version downloads are available at the bottom of the page.
When you use these files, be sure to COMPLETELY UNINSTALL your current version of STC Port Host Controller and then do a FRESH INSTALL of the version included with this update. Failure to do so can result in loss of audio in digital mode!