Me parece que a salida es estéreo, al menos en mi configuración, tengo raspbian instalado y si le tiro un comando amixer obtengo esto en la salida:
pedro@raspberrypi ~ $ amixer
Simple mixer control 'Master',0
Capabilities: pvolume pswitch pswitch-joined penum
Playback channels: Front Left - Front Right
Limits: Playback 0 - 65536
Mono:
Front Left: Playback 42853 [65%] [on]
Front Right: Playback 42853 [65%] [on]
Simple mixer control 'Capture',0
Capabilities: cvolume cswitch cswitch-joined penum
Capture channels: Front Left - Front Right
Limits: Capture 0 - 65536
Front Left: Capture 65536 [100%] [on]
Front Right: Capture 65536 [100%] [on]