Try one cable from Mono output from kb to 1/4 inch jack on right side of Bose. Make sure the switch is down and not on guitar. The sound should more or less duplicate your kb sound.

It certainly should not sound tinny.

Bernie
_________________________
pa4X 76 ,SX900, Audya 76,Yamaha S970 , vArranger, Hammond SK1, Ketron SD40, Centerpoint Space Station, Bose compact