Yamaha YDP-S52 - Manual (Page 13)

Playing Back MIDI Files including Songs Transferred from a Computer
13
Computer-related Operations
To set Playback Channels to “All”:
While holding down [DEMO/SONG] and the [PIANO/VOICE] simultaneously, press the B6 key.
With this operation, the Song data of all channels will be played back.
B6
Highest key