I also do have an issue with digital sound over the optical link (SPdif or TOSlink whatever you want to call it).
This is however intermittent. As I do not have an exact description how to reproduce this I did not want to put it in the thread but since the discussion here is about losing audio entirely here we go:
Configuration SMT FW579, optical TOSlink connection to JVC hometheatre system and HDMI connection to Samsung TV.
Watching a recorded program with digital sound over optical connection to the hometheatre system. After searching for the next chapter (skip adds) with the arrow keys sometimes digital sound over optical connection is dead. Sound over the HDMI connection is available.
Even a (few seconds) full power off with the switch at the back of the SMT does not recover the TOSlink sound.
If we continue to watch the programm with the sound over the HDMI connection to the TV suddenly the optical connection comes to life again (It takes several minutes to recover but how long is unknown at this time).
The issue looks to come up when you overshoot skipping to the next scene and go back a few seconds/minutes, also with the arrow buttons. The issue is as far as I know not observed if you fast-forward or fast-reverse.
So as workaround we skip the major part of the adds with the arrow buttons and seek the exact start point of the next chapter with fast-forward/fast-reverse.
PS, as IT-customer service engineer I admire your communication towards your customers.
regards,
Rik