Updated to version 6.4.42. In the music player, SACD set the playback priority to MCH. When playing an ISO file, the player sees both 2 channels and 6 channels. However, plays only in stereo. The media player is connected to the Yamaha receiver RX-V557 an SPDIF cable. What an explanation might be.
HDMI Audio is set to RAW or Auto? Not PCM (2CH) being the default? Playback of SACD preference in MP7 set to MCH (not 2CH). Pressing the Audio key on the Remote Control will also toggle both modes.
My sound is transmitted to the receiver via an optical connection (it is exposed RAW), and not via HDMI. Maybe that's why there is no MCH playback.