Hello, I am having a similar problem all of a sudden. I have an Nvidia Shield TV that I have been running to a Polk sound bar and an Epson Home Cinema 1060 through an HDMI to HDMI + Optical Audio converter for several years now. All of a sudden, a few weeks ago, it stopped functioning properly.
Currently only 5.1 (digital?) audio will pass through the converter. Any other type of audio won't play. There is a 5.1 option and a pass through option on the converter. When I use passthrough, the audio is choppy, out of sync, and fuzzy. It is correct when I use the 5.1 option on the converter. The problem is the same when I use the projectors inherent audio function and when I use the Polk sound bar connected with the optical cable.
It seems like either the Shield is not sending out the right audio signal or the HDMI cord is not transmitting the signal correctly. I have tried to run the HDMI cord directly to the projector but the same issue is happening, except that when I run the signal through the converter it will properly decode the 5.1 audio, so I don't think the issue is HCDP unless I need a newer HDMI cord?
Sorry for any misuse of terms, I don't know much about audio so this has been a really frustrating learning experience.