What you could do is to load up the Syphon feed into the Media Bank (you can do this by right-clicking, or control-clicking, an empty Media Bank slot and selecting the appropriate Syphon source. Next, set MixEmergency to load a random media item from the Media Bank when and audio file is loaded. If it's the only source in the Media Bank, then it'll get loaded each time an audio-only track is loaded.
