Situation: HTPC should be connected with a Toslink output, which both to an AV receiver, as well as to an external headphone amplifier.
0.5 meters from the Toslink HTPC in the clutch and each 2 meter Toslink from the coupling to the external devices.
Result. Clear signal, no dropouts. Both devices (AV receiver / headphone amplifier) work separately and even at the same time without any problems!