Eddie Williams had the answers:

LSB=0, MSB=16, Pgm Chg = 0 thru 39
for user sounds 1 thru 40. I use the same hex string coding that I mentioned previously.

This worked great. I originally forgot to reset MSB back to 32, which is used for most "regular" (internal) sounds. Once I did that, everything worked great. Now I can call up any sound I want, with one button press, for my external MIDI controller keyboard.