I'm unable to find the music crossfading option in the newest version of AGS. It doesn't seem to be in General Settings or the Properties pane for either the main Audio section or in the Music folder.
Does anybody know if this option is still there and where I can find it?
All of the documentation I can find points to General Settings, but this seems to be outdated information from before the audio system was re-vamped.
You can use
SetGameOption(OPT_CROSSFADEMUSIC, 3); // medium
http://www.adventuregamestudio.co.uk/manual/SetGameOption.htm