I read the post at your link, very interresting. I think I was most curious as to how a guy modeling 1880s narrow gauge steam would have a use for diesel sound! Anyway, your method will work for a small layout, but I don't see it working like you want it to on a freemo module. As soon as you join up with other freemo modules into a layout, your diesel will leave the sound behind when it leaves the sound equipped module. I'm wondering if Athearn makes a dummy version of the gp40-2, and would you be able to fit the sound unit and suitable speakers into a dummy to have the sound follow the train?