I deleted your duplicate post in the other subforum. I think "MIDI" is a good category for it.
Normally a MIDI song file or SMF will contain Program Change messages, and possible Bank Select messages as well, for each MIDI channel that it uses. If the file doesn't contain such messages, you can add them using a MIDI file editor or other utility.
Perhaps the simplest utility for this would be the free "MIDI Revoicer" utility by Jørgen Sørensen, which lets you set and save the voices and a few other basic channel settings-- Volume, Panning, Reverb Depth, and Chorus Depth-- for each of the 16 MIDI channels in a MIDI song file:
MIDI Revoicer - The Unofficial YAMAHA Keyboard Resource Site
I don't know whether the program specifically supports the MO6 as far as having a ready-made list of voices for the MO6, but you can select whichever Program Change and Bank Select values you want, and refer to the Data List or other appropriate document for your keyboard to look up the necessary values for choosing each voice that's available on your keyboard-- even for non-Yamaha keyboards.
Note that you might need to subtract 1 from the Program number that's listed in your keyboard's manual to get the actual Program Change value to use, because Yamaha generally likes to use the 1-128 numbering scheme for Program numbers, whereas the actual values used by the MIDI Program Change message are 0-127.