4K and HDMI splitter outputs sound or audio, not both though.

For the last year I have been using a 4k Apple TV with a high quality monitor (Pioneer Elite) that does not have any sound inputs. To solve the problem I run the Apple TV HDMI into an HDMI splitter, HDMI TV output from the splitter goes to the TV, the splitter digital/optical audio output goes to a Zvox sound bar. Everything worked fine for a year, then all of a sudden I lost the audio, picture was fine. Tried every setting change imaginable, changed out all the cables and even replaced the HDMI splitter. Here is the strange thing, if I disconnect the HDMI video output from the HDMI splitter, sound is restored, no video obviously. If I put the HDMI video cable back in, audio switches off. What has got wrong? HELP