Q: ATV3: How to set audio out to SPDIF?

After updating the Apple TV3 to software version 5.2.1 my amplifier no longer plays the music that should be coming from the Apple TV. I did nothing with the wiring or cables, the only thing that changed is the software update, everything worked fine with the previous software version. I cannot find a menu-option to force audio over the SPDIF to make sure that the Apple TV addresses the right outputs. How can I fix this? Or is it a known issue, to be resolved in a next software update, and I am to do without iTunes music in my livingroom for the time being? Best regards, Bas