The manual reads this at the Multi engine disadventages:
in most cases it’s better to center the two audio channels (especially in poly mode) - stereo sounds can only be realized by using two instruments and assigning them to specific voices (-> see CFG page), but the Lead Engine provides more sophisticated functions for stereo effects!
Does anyone know to best way to center the 2 audio channels so that i do not hear osc 1,2,3 (receiving MIDI at channel 1) at left and osc 4,5,6 (receiving MIDI at channel 2) at right?
Yes - use a mixer or if it’s connected to a DAW software, setup two mono channels using only left in and right in as an input, so you can pan them independently.