Roel,
I do use the SD1 vocalist during live performance and you are right... the output is MONO. The X1 version is also MONO - I'll have to investigate if you could PAN the entire Vocalizer L/R since the entire Keyboard is STEREO, however, within the VOCALIZER itself, you couldn't PAN separate parts L&R eg LEAD voice (L), Harmonies (R)
AJ