After plugging together initially ran only one unit, if the other was unplugged, and turning off the other did nothing. The solution: The cable box is constantly sending a signal at the optical output, even if it was switched on the remote control to standby. When fully shutdown the respective other device functions.
Since one can not blame the adapter, this behavior of the cable box, I give full 5 stars. the bushes are a little stiff but given the low price that's fine.