As to the Converter, Xamarin has been shipping a known-broken version of Mono (v3.10.0) for a month or so now. (See http://stackoverflow.com/a/26685351/147202) There's a fixed version available for download here: https://www.dropbox.com/s/wrjnv7p8zj1rh5u/MonoFramework-MDK-3.10.0.26.macos10.xamarin.x86.pkg?dl=0 (linked indirectly on the StackOverflow page). Installing this version of Mono allowed me to run RocksmithCustomSongToolkit.app.