Soundloader is the Digitrax software for downloading "sound projects" to Digitrax SFX decoders, like the SoundBug and a few others. You need a PR3 unit from Digitrax (or an older PR2) to accomplish this. You can't do it without a computer and one of these programming units.
There is a set of software which controls the sounds. If the software addresses the DIESEL_RUN_HI sound file, then something will happen with it. I don't know whether the software does this. If you can play the sound when you load the project into your computer, my guess is that it does work.
It takes an iron man to play with a toy iron horse.