For anyone interrested. I added both  the EMD GP 38-2 and EMD GP 40  to the Soundtraxx Bachmann SoundValue definition to be included in the next test release of JMRI 4.3.6. 

I worked with someone who had a Bachmann GP 40 SoundValue to get it right as the provided documentation had holes in it.

It was fun figuring out how GITHUB works to get the definition included in the next release.

Marc