On other keyboards I have, when I am in a split mode with the acomp on but not running, I have a sustained chord bass sounding on the left hand in addition to the left voice.

How do I get it ?
pa4X 76 ,SX900, Audya 76,Yamaha S970 , vArranger, Hammond SK1, Ketron SD40, Centerpoint Space Station, Bose compact