With my SD40-2's I went by the book. Turns out the sound board uses CV numbers (some of which) are the same CV numbers that a motor decoder uses. For that reason they use the decoder locking scheme outlined by the NMRA. Before installing the motor decoder set CV16 to a value of 2 for the sound decoder. Then set CV 16 to a value of 1 for the motor decoder. After you install the motor decoder you can program the sound by setting CV15 to 2, back to 0 when done. Likewise you can read and write to the motor decoder by setting CV15 to 1, again set it back to 0 when done.
CV-16 locking codes:
Motor=1
Sound=2
Function =3
Lock disabled=0
When CV-15's value mathes CV-16's locking code that decoder is unlocked.
Example: When CV-15 = 1 you can read/write to the motor decoder.
If you look at the manual you will see that you have to set some sound CV's to enable sound at 4 digit addresses that were programed into the motor decoder. I had loco's that ran great with 4 digit addresses with NO sound until I realized thet fact. After making the correct CV adjustments with th sound decoder "Violla", had sound and every thing fell into place.
Jules
Somewhere in one of the topic threads, the question was raised whether the sound feature of so equipped BLI DC locos would continue to operate correctly after a decoder was installed. For the life of me, I can't track back and find the question and answer.
Would someone please go through the numbers on that again? Mea culpa!