After 15 years... Today I discover that the old ACM pluggin for WinAmp does indeed support mono ACM files! You just elect to configure it in the WinAmp input options, and it asks whether to switch playback modes. (Playing the mono ACMs in stereo mode sounds like Alvin & the Chipmunks) I had no idea. This means that WinAmp can play the Fallout dialog ACMs at normal speed. Music (stereo) mode is the default playback mode; which I used to think was the only mode it supported.