Apparently those voices that I used for the Motif Rack (MSB, LSB and program banks) are different from Motif Rack ES, and I have no idea how/if a sysex could automatically recognize a voice generator (via midi driver) and change the voices on the fly.

Is there a SysEx command that could somehow recognize the voice bank and reroute it to the correct voice on the Rack ES?

It still is a mystery on how I could change the controller (C91) from a type of reverb to another (for example, from “Hall” to something else). Anyone have an example I can use?

The MSB/LSB messages are not System Exclusive but are a category of MIDI messages known as CONTROL CHANGE messages specifically in this case, Bank Select messages.

There is an article in the SUPPORT area that details how these messages work: Bank Select and Program Change Messages and the Motif ES

These messages can recall a specific Voice within a product. The Motif-Rack and the Motif Rack ES are different products so most likely Voices are not going to be in the same exactly locations (even if the Voice is in both products it is not likely that the location would be the same).

No there is no magic command that will do the work for you. New Product means selecting new sounds. Now that said, had you used all USER VOICE locations in the original Motif-Rack, you could have loaded those USER VOICES into the USER banks of the Motif-Rack ES and your sequence would then select the correct sounds. But if you did not, oh well…

It still is a mystery on how I could change the controller (C91) from a type of reverb to another (for example, from “Hall” to something else). Anyone have an example I can use?

Changing the Reverb Type, now that is accomplished with System Exclusive but rather than give yourself a headache typing in System Exclusive messages you simply need to select the new REVERB and store it when you redo your data.