Well, it's easy at all with the Yamaha synth, you have only to send the MSB/LSB and Program together, that's all... For example...
MSB 0 0
LSB 32 0
PRG - 1
I don't know that Banks for MU90R, you have to change the MSB number for sure... That's all... If you don't know the diff. Voices, then go to the yamahasynth.com webside and load the XG Edit down and install it, there you can see ALL Bank Numbers of the sounds you can hear. Maybe you did not see it, but, if you play the piano on Bank #01, and switch to Bank #02 where is no other piano, the Synth is still playing the Piano from Bank#01. On all Banks, there are the same sounds, only some sounds were changed...! It would be easier to check the sounds with the Xg Edit tool, there you can really see which sounds are different..!