When you download a PS/3 sound file, it arrives as a ZIP file. If you unpack it, you'll get two files, the .MTH sound file and another .ZIP file. The ZIP file inside is the chain files, you point the loader at that ZIP file using the icon on the toolbar of the loader. Once the chain files load, power down everything, locomotive and TIU, for around 30 seconds, then fire it up again. If you have changed the content of the chain file, you'll get some Morris code beeps, hopefully the success code.
Load the sound fine the same way you always do.