Yamaha MU90R Owner's Manual page 51

MULTI MODE
Bank Number
Program (Voice) Number
4 2
This determines the bank number of the selected Part's Voice. Each
bank contains 128 Voices. (Refer to the SOUND LIST & MIDI DATA
booklet.)
For more information on selecting banks, see Display Bank Select
parameter, page 118.
This determines the Voice for the selected Part. (Refer to the SOUND
LIST & MIDI DATA booklet.)