Looking for help solving a mystery among TV sound connections here.

Our Samsung TV gets video and sound from two sources—a Spectrum cable box and an Apple TV box. It then sends audio to a stereo amplifier and its speakers through an optical cable that goes from the TV into the Spectrum box, then out through a right and left audio cable (with RCA plugs) into the Aux input on the amp. 

This worked fine for a few weeks, and then sound stopped working for the Apple TV. A long session with Apple on the phone, with lots of changed settings, made no difference. So did switching HDMI inputs, and completely replacing both HDMI cables. Samsung also had no idea when I talked to them on the phone.

The optical connection on the TV is the only way sound gets out to other devices. The AppleTV's only audio-out is through the HDMI connection to the TV.

The Spectrum cable sound works fine. So we know the optical sound from the TV back to the cable box is fine. As is the connection from the cable box to the amp. The whole problem is between the Apple TV box and the Samsung TV.

Any ideas, Lazyweb?