To change the SPDIF format of a session, choose Setups > Playback Engine. In order for us to change I/O labels, a session cannot be opened so when you click yes to proceed your session is automatically saved and closed and after you click done it will reopen your session. You can only use one set of SPDIF ports at a time so if you want to use the coxial SPDIF connection for your Dat machine then you need to set the Optical Format to Adat in the Setups > Playback Engine > Other Options. If you are trying to use a Mini Disc with optical SPDIF that you need to set the Optical Format to SPDIF in the Setups > Playback Engine > Other Options. IF SPDIF mirroring is on, it means that whatever is output to the main outputs 1/2 will also be 'mirrored' on the SPDIF output ports. For some applications you may want to turn off SPDIF mirroring and set the output of a track to the SPDIF outputs.