Mainstage Korg M3 bank select
Bank select MSB/LSB are just standard Control Change messages.

MSB is CC 0 &amp; LSB is CC32 - range is 0 - 127, like any other CC.

Very few devices have what you would consider a 'logical' array of bank numbers; 0, 1, 2, 3 etc, so unless you have a sheet with the banks in Hex or Dec, this is going to be your best method.

Which Bank transmits which Bank Select message?
The simplest way to find out is to just cheat ;-)

Make sure your M3 is set to transmit this data - from the M3 Midi Spec sheet...  


  Notes *P, *A, *C, *E: Transmitted/received when Global P1: MIDI Filter (Program Change, Aftertouch, Control Change, Exclusive) is Enable, respectively


Make sure your DAW is set to record it - I've never used Mainstage, so you'd have to check the manual.

Set your DAW to Record, then hit a bank then program. Check for CC 0 &amp; 32 messages.  

Some devices will transmit the CCs only at the bank change, some will transmit with each program change.
Some will send values for MSB &amp; LSB, some use only one &amp; send 0 for the other.
Some require both MSB &amp; LSB before they will change Bank, some only need one. Some don't change until the Program Change message is sent.

You'll have to experiment to see which your Korg uses.
I have a vague recollection Korg sends something on every button-press, so you might have a fair bit of data to wade through.