The slider is located part of the destinator.bmp file it's located here:
Check if you have another version of destinator.bmp and see if the slider in it is correct (the file is a huge vertical bitmap, the sliders are on the left side.) If you don't have another version, send me a pm, I've got about 6 versions.
You can set the muting percentage in the configuration of destinator itself. (just start it without using FD or MM)